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4853 lines
180 KiB
4853 lines
180 KiB
=head1 NAME
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perlfunc - Perl builtin functions
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=head1 DESCRIPTION
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The functions in this section can serve as terms in an expression.
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They fall into two major categories: list operators and named unary
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operators. These differ in their precedence relationship with a
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following comma. (See the precedence table in L<perlop>.) List
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operators take more than one argument, while unary operators can never
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take more than one argument. Thus, a comma terminates the argument of
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a unary operator, but merely separates the arguments of a list
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operator. A unary operator generally provides a scalar context to its
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argument, while a list operator may provide either scalar or list
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contexts for its arguments. If it does both, the scalar arguments will
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be first, and the list argument will follow. (Note that there can ever
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be only one such list argument.) For instance, splice() has three scalar
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arguments followed by a list, whereas gethostbyname() has four scalar
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arguments.
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In the syntax descriptions that follow, list operators that expect a
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list (and provide list context for the elements of the list) are shown
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with LIST as an argument. Such a list may consist of any combination
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of scalar arguments or list values; the list values will be included
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in the list as if each individual element were interpolated at that
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point in the list, forming a longer single-dimensional list value.
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Elements of the LIST should be separated by commas.
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Any function in the list below may be used either with or without
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parentheses around its arguments. (The syntax descriptions omit the
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parentheses.) If you use the parentheses, the simple (but occasionally
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surprising) rule is this: It I<LOOKS> like a function, therefore it I<IS> a
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function, and precedence doesn't matter. Otherwise it's a list
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operator or unary operator, and precedence does matter. And whitespace
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between the function and left parenthesis doesn't count--so you need to
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be careful sometimes:
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print 1+2+4; # Prints 7.
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print(1+2) + 4; # Prints 3.
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print (1+2)+4; # Also prints 3!
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print +(1+2)+4; # Prints 7.
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print ((1+2)+4); # Prints 7.
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If you run Perl with the B<-w> switch it can warn you about this. For
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example, the third line above produces:
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print (...) interpreted as function at - line 1.
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Useless use of integer addition in void context at - line 1.
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A few functions take no arguments at all, and therefore work as neither
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unary nor list operators. These include such functions as C<time>
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and C<endpwent>. For example, C<time+86_400> always means
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C<time() + 86_400>.
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For functions that can be used in either a scalar or list context,
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nonabortive failure is generally indicated in a scalar context by
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returning the undefined value, and in a list context by returning the
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null list.
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Remember the following important rule: There is B<no rule> that relates
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the behavior of an expression in list context to its behavior in scalar
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context, or vice versa. It might do two totally different things.
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Each operator and function decides which sort of value it would be most
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appropriate to return in scalar context. Some operators return the
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length of the list that would have been returned in list context. Some
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operators return the first value in the list. Some operators return the
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last value in the list. Some operators return a count of successful
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operations. In general, they do what you want, unless you want
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consistency.
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An named array in scalar context is quite different from what would at
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first glance appear to be a list in scalar context. You can't get a list
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like C<(1,2,3)> into being in scalar context, because the compiler knows
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the context at compile time. It would generate the scalar comma operator
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there, not the list construction version of the comma. That means it
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was never a list to start with.
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In general, functions in Perl that serve as wrappers for system calls
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of the same name (like chown(2), fork(2), closedir(2), etc.) all return
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true when they succeed and C<undef> otherwise, as is usually mentioned
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in the descriptions below. This is different from the C interfaces,
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which return C<-1> on failure. Exceptions to this rule are C<wait()>,
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C<waitpid()>, and C<syscall()>. System calls also set the special C<$!>
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variable on failure. Other functions do not, except accidentally.
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=head2 Perl Functions by Category
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Here are Perl's functions (including things that look like
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functions, like some keywords and named operators)
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arranged by category. Some functions appear in more
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than one place.
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=over
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=item Functions for SCALARs or strings
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C<chomp>, C<chop>, C<chr>, C<crypt>, C<hex>, C<index>, C<lc>, C<lcfirst>,
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C<length>, C<oct>, C<ord>, C<pack>, C<q/STRING/>, C<qq/STRING/>, C<reverse>,
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C<rindex>, C<sprintf>, C<substr>, C<tr///>, C<uc>, C<ucfirst>, C<y///>
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=item Regular expressions and pattern matching
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C<m//>, C<pos>, C<quotemeta>, C<s///>, C<split>, C<study>, C<qr//>
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=item Numeric functions
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C<abs>, C<atan2>, C<cos>, C<exp>, C<hex>, C<int>, C<log>, C<oct>, C<rand>,
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C<sin>, C<sqrt>, C<srand>
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=item Functions for real @ARRAYs
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C<pop>, C<push>, C<shift>, C<splice>, C<unshift>
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=item Functions for list data
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C<grep>, C<join>, C<map>, C<qw/STRING/>, C<reverse>, C<sort>, C<unpack>
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=item Functions for real %HASHes
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C<delete>, C<each>, C<exists>, C<keys>, C<values>
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=item Input and output functions
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C<binmode>, C<close>, C<closedir>, C<dbmclose>, C<dbmopen>, C<die>, C<eof>,
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C<fileno>, C<flock>, C<format>, C<getc>, C<print>, C<printf>, C<read>,
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C<readdir>, C<rewinddir>, C<seek>, C<seekdir>, C<select>, C<syscall>,
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C<sysread>, C<sysseek>, C<syswrite>, C<tell>, C<telldir>, C<truncate>,
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C<warn>, C<write>
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=item Functions for fixed length data or records
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C<pack>, C<read>, C<syscall>, C<sysread>, C<syswrite>, C<unpack>, C<vec>
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=item Functions for filehandles, files, or directories
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C<-I<X>>, C<chdir>, C<chmod>, C<chown>, C<chroot>, C<fcntl>, C<glob>,
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C<ioctl>, C<link>, C<lstat>, C<mkdir>, C<open>, C<opendir>,
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C<readlink>, C<rename>, C<rmdir>, C<stat>, C<symlink>, C<umask>,
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C<unlink>, C<utime>
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=item Keywords related to the control flow of your perl program
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C<caller>, C<continue>, C<die>, C<do>, C<dump>, C<eval>, C<exit>,
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C<goto>, C<last>, C<next>, C<redo>, C<return>, C<sub>, C<wantarray>
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=item Keywords related to scoping
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C<caller>, C<import>, C<local>, C<my>, C<package>, C<use>
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=item Miscellaneous functions
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C<defined>, C<dump>, C<eval>, C<formline>, C<local>, C<my>, C<reset>,
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C<scalar>, C<undef>, C<wantarray>
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=item Functions for processes and process groups
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C<alarm>, C<exec>, C<fork>, C<getpgrp>, C<getppid>, C<getpriority>, C<kill>,
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C<pipe>, C<qx/STRING/>, C<setpgrp>, C<setpriority>, C<sleep>, C<system>,
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C<times>, C<wait>, C<waitpid>
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=item Keywords related to perl modules
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C<do>, C<import>, C<no>, C<package>, C<require>, C<use>
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=item Keywords related to classes and object-orientedness
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C<bless>, C<dbmclose>, C<dbmopen>, C<package>, C<ref>, C<tie>, C<tied>,
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C<untie>, C<use>
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=item Low-level socket functions
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C<accept>, C<bind>, C<connect>, C<getpeername>, C<getsockname>,
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C<getsockopt>, C<listen>, C<recv>, C<send>, C<setsockopt>, C<shutdown>,
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C<socket>, C<socketpair>
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=item System V interprocess communication functions
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C<msgctl>, C<msgget>, C<msgrcv>, C<msgsnd>, C<semctl>, C<semget>, C<semop>,
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C<shmctl>, C<shmget>, C<shmread>, C<shmwrite>
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=item Fetching user and group info
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C<endgrent>, C<endhostent>, C<endnetent>, C<endpwent>, C<getgrent>,
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C<getgrgid>, C<getgrnam>, C<getlogin>, C<getpwent>, C<getpwnam>,
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C<getpwuid>, C<setgrent>, C<setpwent>
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=item Fetching network info
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C<endprotoent>, C<endservent>, C<gethostbyaddr>, C<gethostbyname>,
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C<gethostent>, C<getnetbyaddr>, C<getnetbyname>, C<getnetent>,
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C<getprotobyname>, C<getprotobynumber>, C<getprotoent>,
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C<getservbyname>, C<getservbyport>, C<getservent>, C<sethostent>,
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C<setnetent>, C<setprotoent>, C<setservent>
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=item Time-related functions
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C<gmtime>, C<localtime>, C<time>, C<times>
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=item Functions new in perl5
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C<abs>, C<bless>, C<chomp>, C<chr>, C<exists>, C<formline>, C<glob>,
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C<import>, C<lc>, C<lcfirst>, C<map>, C<my>, C<no>, C<prototype>, C<qx>,
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C<qw>, C<readline>, C<readpipe>, C<ref>, C<sub*>, C<sysopen>, C<tie>,
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C<tied>, C<uc>, C<ucfirst>, C<untie>, C<use>
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* - C<sub> was a keyword in perl4, but in perl5 it is an
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operator, which can be used in expressions.
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=item Functions obsoleted in perl5
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C<dbmclose>, C<dbmopen>
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=back
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=head2 Portability
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Perl was born in Unix and can therefore access all common Unix
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system calls. In non-Unix environments, the functionality of some
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Unix system calls may not be available, or details of the available
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functionality may differ slightly. The Perl functions affected
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by this are:
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C<-X>, C<binmode>, C<chmod>, C<chown>, C<chroot>, C<crypt>,
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C<dbmclose>, C<dbmopen>, C<dump>, C<endgrent>, C<endhostent>,
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C<endnetent>, C<endprotoent>, C<endpwent>, C<endservent>, C<exec>,
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C<fcntl>, C<flock>, C<fork>, C<getgrent>, C<getgrgid>, C<gethostent>,
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C<getlogin>, C<getnetbyaddr>, C<getnetbyname>, C<getnetent>,
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C<getppid>, C<getprgp>, C<getpriority>, C<getprotobynumber>,
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C<getprotoent>, C<getpwent>, C<getpwnam>, C<getpwuid>,
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C<getservbyport>, C<getservent>, C<getsockopt>, C<glob>, C<ioctl>,
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C<kill>, C<link>, C<lstat>, C<msgctl>, C<msgget>, C<msgrcv>,
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C<msgsnd>, C<open>, C<pipe>, C<readlink>, C<rename>, C<select>, C<semctl>,
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C<semget>, C<semop>, C<setgrent>, C<sethostent>, C<setnetent>,
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C<setpgrp>, C<setpriority>, C<setprotoent>, C<setpwent>,
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C<setservent>, C<setsockopt>, C<shmctl>, C<shmget>, C<shmread>,
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C<shmwrite>, C<socket>, C<socketpair>, C<stat>, C<symlink>, C<syscall>,
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C<sysopen>, C<system>, C<times>, C<truncate>, C<umask>, C<unlink>,
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C<utime>, C<wait>, C<waitpid>
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For more information about the portability of these functions, see
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L<perlport> and other available platform-specific documentation.
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=head2 Alphabetical Listing of Perl Functions
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=over 8
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=item I<-X> FILEHANDLE
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=item I<-X> EXPR
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=item I<-X>
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A file test, where X is one of the letters listed below. This unary
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operator takes one argument, either a filename or a filehandle, and
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tests the associated file to see if something is true about it. If the
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argument is omitted, tests C<$_>, except for C<-t>, which tests STDIN.
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Unless otherwise documented, it returns C<1> for TRUE and C<''> for FALSE, or
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the undefined value if the file doesn't exist. Despite the funny
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names, precedence is the same as any other named unary operator, and
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the argument may be parenthesized like any other unary operator. The
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operator may be any of:
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X<-r>X<-w>X<-x>X<-o>X<-R>X<-W>X<-X>X<-O>X<-e>X<-z>X<-s>X<-f>X<-d>X<-l>X<-p>
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X<-S>X<-b>X<-c>X<-t>X<-u>X<-g>X<-k>X<-T>X<-B>X<-M>X<-A>X<-C>
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-r File is readable by effective uid/gid.
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-w File is writable by effective uid/gid.
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-x File is executable by effective uid/gid.
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-o File is owned by effective uid.
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-R File is readable by real uid/gid.
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-W File is writable by real uid/gid.
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-X File is executable by real uid/gid.
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-O File is owned by real uid.
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-e File exists.
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-z File has zero size.
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-s File has nonzero size (returns size).
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-f File is a plain file.
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-d File is a directory.
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-l File is a symbolic link.
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-p File is a named pipe (FIFO), or Filehandle is a pipe.
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-S File is a socket.
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-b File is a block special file.
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-c File is a character special file.
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-t Filehandle is opened to a tty.
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-u File has setuid bit set.
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-g File has setgid bit set.
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-k File has sticky bit set.
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-T File is a text file.
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-B File is a binary file (opposite of -T).
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-M Age of file in days when script started.
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-A Same for access time.
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-C Same for inode change time.
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Example:
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while (<>) {
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chop;
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next unless -f $_; # ignore specials
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#...
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}
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The interpretation of the file permission operators C<-r>, C<-R>,
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C<-w>, C<-W>, C<-x>, and C<-X> is by default based solely on the mode
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of the file and the uids and gids of the user. There may be other
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reasons you can't actually read, write, or execute the file. Such
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reasons may be for example network filesystem access controls, ACLs
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(access control lists), read-only filesystems, and unrecognized
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executable formats.
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Also note that, for the superuser on the local filesystems, the C<-r>,
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C<-R>, C<-w>, and C<-W> tests always return 1, and C<-x> and C<-X> return 1
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if any execute bit is set in the mode. Scripts run by the superuser
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may thus need to do a stat() to determine the actual mode of the file,
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or temporarily set their effective uid to something else.
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Note that C<-s/a/b/> does not do a negated substitution. Saying
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C<-exp($foo)> still works as expected, however--only single letters
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following a minus are interpreted as file tests.
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The C<-T> and C<-B> switches work as follows. The first block or so of the
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file is examined for odd characters such as strange control codes or
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characters with the high bit set. If too many strange characters (E<gt>30%)
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are found, it's a C<-B> file, otherwise it's a C<-T> file. Also, any file
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containing null in the first block is considered a binary file. If C<-T>
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or C<-B> is used on a filehandle, the current stdio buffer is examined
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rather than the first block. Both C<-T> and C<-B> return TRUE on a null
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file, or a file at EOF when testing a filehandle. Because you have to
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read a file to do the C<-T> test, on most occasions you want to use a C<-f>
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against the file first, as in C<next unless -f $file && -T $file>.
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If any of the file tests (or either the C<stat()> or C<lstat()> operators) are given
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the special filehandle consisting of a solitary underline, then the stat
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structure of the previous file test (or stat operator) is used, saving
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a system call. (This doesn't work with C<-t>, and you need to remember
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that lstat() and C<-l> will leave values in the stat structure for the
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symbolic link, not the real file.) Example:
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print "Can do.\n" if -r $a || -w _ || -x _;
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stat($filename);
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print "Readable\n" if -r _;
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print "Writable\n" if -w _;
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print "Executable\n" if -x _;
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print "Setuid\n" if -u _;
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print "Setgid\n" if -g _;
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print "Sticky\n" if -k _;
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print "Text\n" if -T _;
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print "Binary\n" if -B _;
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=item abs VALUE
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=item abs
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Returns the absolute value of its argument.
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If VALUE is omitted, uses C<$_>.
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=item accept NEWSOCKET,GENERICSOCKET
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Accepts an incoming socket connect, just as the accept(2) system call
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does. Returns the packed address if it succeeded, FALSE otherwise.
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See the example in L<perlipc/"Sockets: Client/Server Communication">.
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=item alarm SECONDS
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=item alarm
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Arranges to have a SIGALRM delivered to this process after the
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specified number of seconds have elapsed. If SECONDS is not specified,
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the value stored in C<$_> is used. (On some machines,
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unfortunately, the elapsed time may be up to one second less than you
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specified because of how seconds are counted.) Only one timer may be
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counting at once. Each call disables the previous timer, and an
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argument of C<0> may be supplied to cancel the previous timer without
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starting a new one. The returned value is the amount of time remaining
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on the previous timer.
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For delays of finer granularity than one second, you may use Perl's
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four-arugment version of select() leaving the first three arguments
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undefined, or you might be able to use the C<syscall()> interface to
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access setitimer(2) if your system supports it. The Time::HiRes module
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from CPAN may also prove useful.
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It is usually a mistake to intermix C<alarm()>
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and C<sleep()> calls.
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If you want to use C<alarm()> to time out a system call you need to use an
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C<eval()>/C<die()> pair. You can't rely on the alarm causing the system call to
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fail with C<$!> set to C<EINTR> because Perl sets up signal handlers to
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restart system calls on some systems. Using C<eval()>/C<die()> always works,
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modulo the caveats given in L<perlipc/"Signals">.
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eval {
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local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required
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alarm $timeout;
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$nread = sysread SOCKET, $buffer, $size;
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alarm 0;
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};
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if ($@) {
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die unless $@ eq "alarm\n"; # propagate unexpected errors
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# timed out
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}
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else {
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# didn't
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}
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=item atan2 Y,X
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Returns the arctangent of Y/X in the range -PI to PI.
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For the tangent operation, you may use the C<POSIX::tan()>
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function, or use the familiar relation:
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sub tan { sin($_[0]) / cos($_[0]) }
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=item bind SOCKET,NAME
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Binds a network address to a socket, just as the bind system call
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does. Returns TRUE if it succeeded, FALSE otherwise. NAME should be a
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packed address of the appropriate type for the socket. See the examples in
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L<perlipc/"Sockets: Client/Server Communication">.
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=item binmode FILEHANDLE
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|
|
Arranges for the file to be read or written in "binary" mode in operating
|
|
systems that distinguish between binary and text files. Files that
|
|
are not in binary mode have CR LF sequences translated to LF on input
|
|
and LF translated to CR LF on output. Binmode has no effect under
|
|
many sytems, but in MS-DOS and similarly archaic systems, it may be
|
|
imperative--otherwise your MS-DOS-damaged C library may mangle your file.
|
|
The key distinction between systems that need C<binmode()> and those
|
|
that don't is their text file formats. Systems like Unix, MacOS, and
|
|
Plan9 that delimit lines with a single character, and that encode that
|
|
character in C as C<"\n">, do not need C<binmode()>. The rest may need it.
|
|
If FILEHANDLE is an expression, the value is taken as the name of the
|
|
filehandle.
|
|
|
|
If the system does care about it, using it when you shouldn't is just as
|
|
perilous as failing to use it when you should. Fortunately for most of
|
|
us, you can't go wrong using binmode() on systems that don't care about
|
|
it, though.
|
|
|
|
=item bless REF,CLASSNAME
|
|
|
|
=item bless REF
|
|
|
|
This function tells the thingy referenced by REF that it is now an object
|
|
in the CLASSNAME package. If CLASSNAME is omitted, the current package
|
|
is used. Because a C<bless()> is often the last thing in a constructor.
|
|
it returns the reference for convenience. Always use the two-argument
|
|
version if the function doing the blessing might be inherited by a
|
|
derived class. See L<perltoot> and L<perlobj> for more about the blessing
|
|
(and blessings) of objects.
|
|
|
|
Consider always blessing objects in CLASSNAMEs that are mixed case.
|
|
Namespaces with all lowercase names are considered reserved for
|
|
Perl pragmata. Builtin types have all uppercase names, so to prevent
|
|
confusion, you may wish to avoid such package names as well. Make sure
|
|
that CLASSNAME is a true value.
|
|
|
|
See L<perlmod/"Perl Modules">.
|
|
|
|
=item caller EXPR
|
|
|
|
=item caller
|
|
|
|
Returns the context of the current subroutine call. In scalar context,
|
|
returns the caller's package name if there is a caller, that is, if
|
|
we're in a subroutine or C<eval()> or C<require()>, and the undefined value
|
|
otherwise. In list context, returns
|
|
|
|
($package, $filename, $line) = caller;
|
|
|
|
With EXPR, it returns some extra information that the debugger uses to
|
|
print a stack trace. The value of EXPR indicates how many call frames
|
|
to go back before the current one.
|
|
|
|
($package, $filename, $line, $subroutine,
|
|
$hasargs, $wantarray, $evaltext, $is_require) = caller($i);
|
|
|
|
Here C<$subroutine> may be C<"(eval)"> if the frame is not a subroutine
|
|
call, but an C<eval()>. In such a case additional elements C<$evaltext> and
|
|
C<$is_require> are set: C<$is_require> is true if the frame is created by a
|
|
C<require> or C<use> statement, C<$evaltext> contains the text of the
|
|
C<eval EXPR> statement. In particular, for a C<eval BLOCK> statement,
|
|
C<$filename> is C<"(eval)">, but C<$evaltext> is undefined. (Note also that
|
|
each C<use> statement creates a C<require> frame inside an C<eval EXPR>)
|
|
frame.
|
|
|
|
Furthermore, when called from within the DB package, caller returns more
|
|
detailed information: it sets the list variable C<@DB::args> to be the
|
|
arguments with which the subroutine was invoked.
|
|
|
|
Be aware that the optimizer might have optimized call frames away before
|
|
C<caller()> had a chance to get the information. That means that C<caller(N)>
|
|
might not return information about the call frame you expect it do, for
|
|
C<N E<gt> 1>. In particular, C<@DB::args> might have information from the
|
|
previous time C<caller()> was called.
|
|
|
|
=item chdir EXPR
|
|
|
|
Changes the working directory to EXPR, if possible. If EXPR is omitted,
|
|
changes to the user's home directory. Returns TRUE upon success,
|
|
FALSE otherwise. See the example under C<die()>.
|
|
|
|
=item chmod LIST
|
|
|
|
Changes the permissions of a list of files. The first element of the
|
|
list must be the numerical mode, which should probably be an octal
|
|
number, and which definitely should I<not> a string of octal digits:
|
|
C<0644> is okay, C<'0644'> is not. Returns the number of files
|
|
successfully changed. See also L</oct>, if all you have is a string.
|
|
|
|
$cnt = chmod 0755, 'foo', 'bar';
|
|
chmod 0755, @executables;
|
|
$mode = '0644'; chmod $mode, 'foo'; # !!! sets mode to
|
|
# --w----r-T
|
|
$mode = '0644'; chmod oct($mode), 'foo'; # this is better
|
|
$mode = 0644; chmod $mode, 'foo'; # this is best
|
|
|
|
=item chomp VARIABLE
|
|
|
|
=item chomp LIST
|
|
|
|
=item chomp
|
|
|
|
This safer version of L</chop> removes any trailing string
|
|
that corresponds to the current value of C<$/> (also known as
|
|
$INPUT_RECORD_SEPARATOR in the C<English> module). It returns the total
|
|
number of characters removed from all its arguments. It's often used to
|
|
remove the newline from the end of an input record when you're worried
|
|
that the final record may be missing its newline. When in paragraph
|
|
mode (C<$/ = "">), it removes all trailing newlines from the string.
|
|
If VARIABLE is omitted, it chomps C<$_>. Example:
|
|
|
|
while (<>) {
|
|
chomp; # avoid \n on last field
|
|
@array = split(/:/);
|
|
# ...
|
|
}
|
|
|
|
You can actually chomp anything that's an lvalue, including an assignment:
|
|
|
|
chomp($cwd = `pwd`);
|
|
chomp($answer = <STDIN>);
|
|
|
|
If you chomp a list, each element is chomped, and the total number of
|
|
characters removed is returned.
|
|
|
|
=item chop VARIABLE
|
|
|
|
=item chop LIST
|
|
|
|
=item chop
|
|
|
|
Chops off the last character of a string and returns the character
|
|
chopped. It's used primarily to remove the newline from the end of an
|
|
input record, but is much more efficient than C<s/\n//> because it neither
|
|
scans nor copies the string. If VARIABLE is omitted, chops C<$_>.
|
|
Example:
|
|
|
|
while (<>) {
|
|
chop; # avoid \n on last field
|
|
@array = split(/:/);
|
|
#...
|
|
}
|
|
|
|
You can actually chop anything that's an lvalue, including an assignment:
|
|
|
|
chop($cwd = `pwd`);
|
|
chop($answer = <STDIN>);
|
|
|
|
If you chop a list, each element is chopped. Only the value of the
|
|
last C<chop()> is returned.
|
|
|
|
Note that C<chop()> returns the last character. To return all but the last
|
|
character, use C<substr($string, 0, -1)>.
|
|
|
|
=item chown LIST
|
|
|
|
Changes the owner (and group) of a list of files. The first two
|
|
elements of the list must be the I<NUMERICAL> uid and gid, in that order.
|
|
Returns the number of files successfully changed.
|
|
|
|
$cnt = chown $uid, $gid, 'foo', 'bar';
|
|
chown $uid, $gid, @filenames;
|
|
|
|
Here's an example that looks up nonnumeric uids in the passwd file:
|
|
|
|
print "User: ";
|
|
chop($user = <STDIN>);
|
|
print "Files: ";
|
|
chop($pattern = <STDIN>);
|
|
|
|
($login,$pass,$uid,$gid) = getpwnam($user)
|
|
or die "$user not in passwd file";
|
|
|
|
@ary = glob($pattern); # expand filenames
|
|
chown $uid, $gid, @ary;
|
|
|
|
On most systems, you are not allowed to change the ownership of the
|
|
file unless you're the superuser, although you should be able to change
|
|
the group to any of your secondary groups. On insecure systems, these
|
|
restrictions may be relaxed, but this is not a portable assumption.
|
|
|
|
=item chr NUMBER
|
|
|
|
=item chr
|
|
|
|
Returns the character represented by that NUMBER in the character set.
|
|
For example, C<chr(65)> is C<"A"> in ASCII. For the reverse, use L</ord>.
|
|
|
|
If NUMBER is omitted, uses C<$_>.
|
|
|
|
=item chroot FILENAME
|
|
|
|
=item chroot
|
|
|
|
This function works like the system call by the same name: it makes the
|
|
named directory the new root directory for all further pathnames that
|
|
begin with a C<"/"> by your process and all its children. (It doesn't
|
|
change your current working directory, which is unaffected.) For security
|
|
reasons, this call is restricted to the superuser. If FILENAME is
|
|
omitted, does a C<chroot()> to C<$_>.
|
|
|
|
=item close FILEHANDLE
|
|
|
|
=item close
|
|
|
|
Closes the file or pipe associated with the file handle, returning TRUE
|
|
only if stdio successfully flushes buffers and closes the system file
|
|
descriptor. Closes the currently selected filehandle if the argument
|
|
is omitted.
|
|
|
|
You don't have to close FILEHANDLE if you are immediately going to do
|
|
another C<open()> on it, because C<open()> will close it for you. (See
|
|
C<open()>.) However, an explicit C<close()> on an input file resets the line
|
|
counter (C<$.>), while the implicit close done by C<open()> does not.
|
|
|
|
If the file handle came from a piped open C<close()> will additionally
|
|
return FALSE if one of the other system calls involved fails or if the
|
|
program exits with non-zero status. (If the only problem was that the
|
|
program exited non-zero C<$!> will be set to C<0>.) Closing a pipe
|
|
also waits for the process executing on the pipe to complete, in case you
|
|
want to look at the output of the pipe afterwards, and
|
|
implicitly puts the exit status value of that command into C<$?>.
|
|
|
|
Example:
|
|
|
|
open(OUTPUT, '|sort >foo') # pipe to sort
|
|
or die "Can't start sort: $!";
|
|
#... # print stuff to output
|
|
close OUTPUT # wait for sort to finish
|
|
or warn $! ? "Error closing sort pipe: $!"
|
|
: "Exit status $? from sort";
|
|
open(INPUT, 'foo') # get sort's results
|
|
or die "Can't open 'foo' for input: $!";
|
|
|
|
FILEHANDLE may be an expression whose value can be used as an indirect
|
|
filehandle, usually the real filehandle name.
|
|
|
|
=item closedir DIRHANDLE
|
|
|
|
Closes a directory opened by C<opendir()> and returns the success of that
|
|
system call.
|
|
|
|
DIRHANDLE may be an expression whose value can be used as an indirect
|
|
dirhandle, usually the real dirhandle name.
|
|
|
|
=item connect SOCKET,NAME
|
|
|
|
Attempts to connect to a remote socket, just as the connect system call
|
|
does. Returns TRUE if it succeeded, FALSE otherwise. NAME should be a
|
|
packed address of the appropriate type for the socket. See the examples in
|
|
L<perlipc/"Sockets: Client/Server Communication">.
|
|
|
|
=item continue BLOCK
|
|
|
|
Actually a flow control statement rather than a function. If there is a
|
|
C<continue> BLOCK attached to a BLOCK (typically in a C<while> or
|
|
C<foreach>), it is always executed just before the conditional is about to
|
|
be evaluated again, just like the third part of a C<for> loop in C. Thus
|
|
it can be used to increment a loop variable, even when the loop has been
|
|
continued via the C<next> statement (which is similar to the C C<continue>
|
|
statement).
|
|
|
|
C<last>, C<next>, or C<redo> may appear within a C<continue>
|
|
block. C<last> and C<redo> will behave as if they had been executed within
|
|
the main block. So will C<next>, but since it will execute a C<continue>
|
|
block, it may be more entertaining.
|
|
|
|
while (EXPR) {
|
|
### redo always comes here
|
|
do_something;
|
|
} continue {
|
|
### next always comes here
|
|
do_something_else;
|
|
# then back the top to re-check EXPR
|
|
}
|
|
### last always comes here
|
|
|
|
Omitting the C<continue> section is semantically equivalent to using an
|
|
empty one, logically enough. In that case, C<next> goes directly back
|
|
to check the condition at the top of the loop.
|
|
|
|
=item cos EXPR
|
|
|
|
Returns the cosine of EXPR (expressed in radians). If EXPR is omitted,
|
|
takes cosine of C<$_>.
|
|
|
|
For the inverse cosine operation, you may use the C<POSIX::acos()>
|
|
function, or use this relation:
|
|
|
|
sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) }
|
|
|
|
=item crypt PLAINTEXT,SALT
|
|
|
|
Encrypts a string exactly like the crypt(3) function in the C library
|
|
(assuming that you actually have a version there that has not been
|
|
extirpated as a potential munition). This can prove useful for checking
|
|
the password file for lousy passwords, amongst other things. Only the
|
|
guys wearing white hats should do this.
|
|
|
|
Note that C<crypt()> is intended to be a one-way function, much like breaking
|
|
eggs to make an omelette. There is no (known) corresponding decrypt
|
|
function. As a result, this function isn't all that useful for
|
|
cryptography. (For that, see your nearby CPAN mirror.)
|
|
|
|
When verifying an existing encrypted string you should use the encrypted
|
|
text as the salt (like C<crypt($plain, $crypted) eq $crypted>). This
|
|
allows your code to work with the standard C<crypt()> and with more
|
|
exotic implementations. When choosing a new salt create a random two
|
|
character string whose characters come from the set C<[./0-9A-Za-z]>
|
|
(like C<join '', ('.', '/', 0..9, 'A'..'Z', 'a'..'z')[rand 64, rand 64]>).
|
|
|
|
Here's an example that makes sure that whoever runs this program knows
|
|
their own password:
|
|
|
|
$pwd = (getpwuid($<))[1];
|
|
|
|
system "stty -echo";
|
|
print "Password: ";
|
|
chomp($word = <STDIN>);
|
|
print "\n";
|
|
system "stty echo";
|
|
|
|
if (crypt($word, $pwd) ne $pwd) {
|
|
die "Sorry...\n";
|
|
} else {
|
|
print "ok\n";
|
|
}
|
|
|
|
Of course, typing in your own password to whoever asks you
|
|
for it is unwise.
|
|
|
|
=item dbmclose HASH
|
|
|
|
[This function has been largely superseded by the C<untie()> function.]
|
|
|
|
Breaks the binding between a DBM file and a hash.
|
|
|
|
=item dbmopen HASH,DBNAME,MODE
|
|
|
|
[This function has been largely superseded by the C<tie()> function.]
|
|
|
|
This binds a dbm(3), ndbm(3), sdbm(3), gdbm(3), or Berkeley DB file to a
|
|
hash. HASH is the name of the hash. (Unlike normal C<open()>, the first
|
|
argument is I<NOT> a filehandle, even though it looks like one). DBNAME
|
|
is the name of the database (without the F<.dir> or F<.pag> extension if
|
|
any). If the database does not exist, it is created with protection
|
|
specified by MODE (as modified by the C<umask()>). If your system supports
|
|
only the older DBM functions, you may perform only one C<dbmopen()> in your
|
|
program. In older versions of Perl, if your system had neither DBM nor
|
|
ndbm, calling C<dbmopen()> produced a fatal error; it now falls back to
|
|
sdbm(3).
|
|
|
|
If you don't have write access to the DBM file, you can only read hash
|
|
variables, not set them. If you want to test whether you can write,
|
|
either use file tests or try setting a dummy hash entry inside an C<eval()>,
|
|
which will trap the error.
|
|
|
|
Note that functions such as C<keys()> and C<values()> may return huge lists
|
|
when used on large DBM files. You may prefer to use the C<each()>
|
|
function to iterate over large DBM files. Example:
|
|
|
|
# print out history file offsets
|
|
dbmopen(%HIST,'/usr/lib/news/history',0666);
|
|
while (($key,$val) = each %HIST) {
|
|
print $key, ' = ', unpack('L',$val), "\n";
|
|
}
|
|
dbmclose(%HIST);
|
|
|
|
See also L<AnyDBM_File> for a more general description of the pros and
|
|
cons of the various dbm approaches, as well as L<DB_File> for a particularly
|
|
rich implementation.
|
|
|
|
You can control which DBM library you use by loading that library
|
|
before you call dbmopen():
|
|
|
|
use DB_File;
|
|
dbmopen(%NS_Hist, "$ENV{HOME}/.netscape/history.db")
|
|
or die "Can't open netscape history file: $!";
|
|
|
|
=item defined EXPR
|
|
|
|
=item defined
|
|
|
|
Returns a Boolean value telling whether EXPR has a value other than
|
|
the undefined value C<undef>. If EXPR is not present, C<$_> will be
|
|
checked.
|
|
|
|
Many operations return C<undef> to indicate failure, end of file,
|
|
system error, uninitialized variable, and other exceptional
|
|
conditions. This function allows you to distinguish C<undef> from
|
|
other values. (A simple Boolean test will not distinguish among
|
|
C<undef>, zero, the empty string, and C<"0">, which are all equally
|
|
false.) Note that since C<undef> is a valid scalar, its presence
|
|
doesn't I<necessarily> indicate an exceptional condition: C<pop()>
|
|
returns C<undef> when its argument is an empty array, I<or> when the
|
|
element to return happens to be C<undef>.
|
|
|
|
You may also use C<defined()> to check whether a subroutine exists, by
|
|
saying C<defined &func> without parentheses. On the other hand, use
|
|
of C<defined()> upon aggregates (hashes and arrays) is not guaranteed to
|
|
produce intuitive results, and should probably be avoided.
|
|
|
|
When used on a hash element, it tells you whether the value is defined,
|
|
not whether the key exists in the hash. Use L</exists> for the latter
|
|
purpose.
|
|
|
|
Examples:
|
|
|
|
print if defined $switch{'D'};
|
|
print "$val\n" while defined($val = pop(@ary));
|
|
die "Can't readlink $sym: $!"
|
|
unless defined($value = readlink $sym);
|
|
sub foo { defined &$bar ? &$bar(@_) : die "No bar"; }
|
|
$debugging = 0 unless defined $debugging;
|
|
|
|
Note: Many folks tend to overuse C<defined()>, and then are surprised to
|
|
discover that the number C<0> and C<""> (the zero-length string) are, in fact,
|
|
defined values. For example, if you say
|
|
|
|
"ab" =~ /a(.*)b/;
|
|
|
|
The pattern match succeeds, and C<$1> is defined, despite the fact that it
|
|
matched "nothing". But it didn't really match nothing--rather, it
|
|
matched something that happened to be zero characters long. This is all
|
|
very above-board and honest. When a function returns an undefined value,
|
|
it's an admission that it couldn't give you an honest answer. So you
|
|
should use C<defined()> only when you're questioning the integrity of what
|
|
you're trying to do. At other times, a simple comparison to C<0> or C<""> is
|
|
what you want.
|
|
|
|
Currently, using C<defined()> on an entire array or hash reports whether
|
|
memory for that aggregate has ever been allocated. So an array you set
|
|
to the empty list appears undefined initially, and one that once was full
|
|
and that you then set to the empty list still appears defined. You
|
|
should instead use a simple test for size:
|
|
|
|
if (@an_array) { print "has array elements\n" }
|
|
if (%a_hash) { print "has hash members\n" }
|
|
|
|
Using C<undef()> on these, however, does clear their memory and then report
|
|
them as not defined anymore, but you shouldn't do that unless you don't
|
|
plan to use them again, because it saves time when you load them up
|
|
again to have memory already ready to be filled. The normal way to
|
|
free up space used by an aggregate is to assign the empty list.
|
|
|
|
This counterintuitive behavior of C<defined()> on aggregates may be
|
|
changed, fixed, or broken in a future release of Perl.
|
|
|
|
See also L</undef>, L</exists>, L</ref>.
|
|
|
|
=item delete EXPR
|
|
|
|
Deletes the specified key(s) and their associated values from a hash.
|
|
For each key, returns the deleted value associated with that key, or
|
|
the undefined value if there was no such key. Deleting from C<$ENV{}>
|
|
modifies the environment. Deleting from a hash tied to a DBM file
|
|
deletes the entry from the DBM file. (But deleting from a C<tie()>d hash
|
|
doesn't necessarily return anything.)
|
|
|
|
The following deletes all the values of a hash:
|
|
|
|
foreach $key (keys %HASH) {
|
|
delete $HASH{$key};
|
|
}
|
|
|
|
And so does this:
|
|
|
|
delete @HASH{keys %HASH}
|
|
|
|
But both of these are slower than just assigning the empty list
|
|
or undefining it:
|
|
|
|
%hash = (); # completely empty %hash
|
|
undef %hash; # forget %hash every existed
|
|
|
|
Note that the EXPR can be arbitrarily complicated as long as the final
|
|
operation is a hash element lookup or hash slice:
|
|
|
|
delete $ref->[$x][$y]{$key};
|
|
delete @{$ref->[$x][$y]}{$key1, $key2, @morekeys};
|
|
|
|
=item die LIST
|
|
|
|
Outside an C<eval()>, prints the value of LIST to C<STDERR> and exits with
|
|
the current value of C<$!> (errno). If C<$!> is C<0>, exits with the value of
|
|
C<($? E<gt>E<gt> 8)> (backtick `command` status). If C<($? E<gt>E<gt> 8)>
|
|
is C<0>, exits with C<255>. Inside an C<eval(),> the error message is stuffed into
|
|
C<$@> and the C<eval()> is terminated with the undefined value. This makes
|
|
C<die()> the way to raise an exception.
|
|
|
|
Equivalent examples:
|
|
|
|
die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news';
|
|
chdir '/usr/spool/news' or die "Can't cd to spool: $!\n"
|
|
|
|
If the value of EXPR does not end in a newline, the current script line
|
|
number and input line number (if any) are also printed, and a newline
|
|
is supplied. Note that the "input line number" (also known as "chunk")
|
|
is subject to whatever notion of "line" happens to be currently in
|
|
effect, and is also available as the special variable C<$.>.
|
|
See L<perlvar/"$/"> and L<perlvar/"$.">.
|
|
|
|
Hint: sometimes appending C<", stopped"> to your message
|
|
will cause it to make better sense when the string C<"at foo line 123"> is
|
|
appended. Suppose you are running script "canasta".
|
|
|
|
die "/etc/games is no good";
|
|
die "/etc/games is no good, stopped";
|
|
|
|
produce, respectively
|
|
|
|
/etc/games is no good at canasta line 123.
|
|
/etc/games is no good, stopped at canasta line 123.
|
|
|
|
See also exit(), warn(), and the Carp module.
|
|
|
|
If LIST is empty and C<$@> already contains a value (typically from a
|
|
previous eval) that value is reused after appending C<"\t...propagated">.
|
|
This is useful for propagating exceptions:
|
|
|
|
eval { ... };
|
|
die unless $@ =~ /Expected exception/;
|
|
|
|
If C<$@> is empty then the string C<"Died"> is used.
|
|
|
|
die() can also be called with a reference argument. If this happens to be
|
|
trapped within an eval(), $@ contains the reference. This behavior permits
|
|
a more elaborate exception handling implementation using objects that
|
|
maintain arbitary state about the nature of the exception. Such a scheme
|
|
is sometimes preferable to matching particular string values of $@ using
|
|
regular expressions. Here's an example:
|
|
|
|
eval { ... ; die Some::Module::Exception->new( FOO => "bar" ) };
|
|
if ($@) {
|
|
if (ref($@) && UNIVERSAL::isa($@,"Some::Module::Exception")) {
|
|
# handle Some::Module::Exception
|
|
}
|
|
else {
|
|
# handle all other possible exceptions
|
|
}
|
|
}
|
|
|
|
Since perl will stringify uncaught exception messages before displaying
|
|
them, you may want to overload stringification operations on such custom
|
|
exception objects. See L<overload> for details about that.
|
|
|
|
You can arrange for a callback to be run just before the C<die()> does
|
|
its deed, by setting the C<$SIG{__DIE__}> hook. The associated handler
|
|
will be called with the error text and can change the error message, if
|
|
it sees fit, by calling C<die()> again. See L<perlvar/$SIG{expr}> for details on
|
|
setting C<%SIG> entries, and L<"eval BLOCK"> for some examples.
|
|
|
|
Note that the C<$SIG{__DIE__}> hook is currently called even inside
|
|
eval()ed blocks/strings! If one wants the hook to do nothing in such
|
|
situations, put
|
|
|
|
die @_ if $^S;
|
|
|
|
as the first line of the handler (see L<perlvar/$^S>). Because this
|
|
promotes action at a distance, this counterintuitive behavior may be fixed
|
|
in a future release.
|
|
|
|
=item do BLOCK
|
|
|
|
Not really a function. Returns the value of the last command in the
|
|
sequence of commands indicated by BLOCK. When modified by a loop
|
|
modifier, executes the BLOCK once before testing the loop condition.
|
|
(On other statements the loop modifiers test the conditional first.)
|
|
|
|
C<do BLOCK> does I<not> count as a loop, so the loop control statements
|
|
C<next>, C<last>, or C<redo> cannot be used to leave or restart the block.
|
|
See L<perlsyn> for alternative strategies.
|
|
|
|
=item do SUBROUTINE(LIST)
|
|
|
|
A deprecated form of subroutine call. See L<perlsub>.
|
|
|
|
=item do EXPR
|
|
|
|
Uses the value of EXPR as a filename and executes the contents of the
|
|
file as a Perl script. Its primary use is to include subroutines
|
|
from a Perl subroutine library.
|
|
|
|
do 'stat.pl';
|
|
|
|
is just like
|
|
|
|
scalar eval `cat stat.pl`;
|
|
|
|
except that it's more efficient and concise, keeps track of the current
|
|
filename for error messages, searches the @INC libraries, and updates
|
|
C<%INC> if the file is found. See L<perlvar/Predefined Names> for these
|
|
variables. It also differs in that code evaluated with C<do FILENAME>
|
|
cannot see lexicals in the enclosing scope; C<eval STRING> does. It's the
|
|
same, however, in that it does reparse the file every time you call it,
|
|
so you probably don't want to do this inside a loop.
|
|
|
|
If C<do> cannot read the file, it returns undef and sets C<$!> to the
|
|
error. If C<do> can read the file but cannot compile it, it
|
|
returns undef and sets an error message in C<$@>. If the file is
|
|
successfully compiled, C<do> returns the value of the last expression
|
|
evaluated.
|
|
|
|
Note that inclusion of library modules is better done with the
|
|
C<use()> and C<require()> operators, which also do automatic error checking
|
|
and raise an exception if there's a problem.
|
|
|
|
You might like to use C<do> to read in a program configuration
|
|
file. Manual error checking can be done this way:
|
|
|
|
# read in config files: system first, then user
|
|
for $file ("/share/prog/defaults.rc",
|
|
"$ENV{HOME}/.someprogrc")
|
|
{
|
|
unless ($return = do $file) {
|
|
warn "couldn't parse $file: $@" if $@;
|
|
warn "couldn't do $file: $!" unless defined $return;
|
|
warn "couldn't run $file" unless $return;
|
|
}
|
|
}
|
|
|
|
=item dump LABEL
|
|
|
|
=item dump
|
|
|
|
This causes an immediate core dump. Primarily this is so that you can
|
|
use the B<undump> program to turn your core dump into an executable binary
|
|
after having initialized all your variables at the beginning of the
|
|
program. When the new binary is executed it will begin by executing a
|
|
C<goto LABEL> (with all the restrictions that C<goto> suffers). Think of
|
|
it as a goto with an intervening core dump and reincarnation. If C<LABEL>
|
|
is omitted, restarts the program from the top. WARNING: Any files
|
|
opened at the time of the dump will NOT be open any more when the
|
|
program is reincarnated, with possible resulting confusion on the part
|
|
of Perl. See also B<-u> option in L<perlrun>.
|
|
|
|
Example:
|
|
|
|
#!/usr/bin/perl
|
|
require 'getopt.pl';
|
|
require 'stat.pl';
|
|
%days = (
|
|
'Sun' => 1,
|
|
'Mon' => 2,
|
|
'Tue' => 3,
|
|
'Wed' => 4,
|
|
'Thu' => 5,
|
|
'Fri' => 6,
|
|
'Sat' => 7,
|
|
);
|
|
|
|
dump QUICKSTART if $ARGV[0] eq '-d';
|
|
|
|
QUICKSTART:
|
|
Getopt('f');
|
|
|
|
This operator is largely obsolete, partly because it's very hard to
|
|
convert a core file into an executable, and because the real perl-to-C
|
|
compiler has superseded it.
|
|
|
|
=item each HASH
|
|
|
|
When called in list context, returns a 2-element list consisting of the
|
|
key and value for the next element of a hash, so that you can iterate over
|
|
it. When called in scalar context, returns the key for only the "next"
|
|
element in the hash. (Note: Keys may be C<"0"> or C<"">, which are logically
|
|
false; you may wish to avoid constructs like C<while ($k = each %foo) {}>
|
|
for this reason.)
|
|
|
|
Entries are returned in an apparently random order. The actual random
|
|
order is subject to change in future versions of perl, but it is guaranteed
|
|
to be in the same order as either the C<keys()> or C<values()> function
|
|
would produce on the same (unmodified) hash.
|
|
|
|
When the hash is entirely read, a null array is returned in list context
|
|
(which when assigned produces a FALSE (C<0>) value), and C<undef> in
|
|
scalar context. The next call to C<each()> after that will start iterating
|
|
again. There is a single iterator for each hash, shared by all C<each()>,
|
|
C<keys()>, and C<values()> function calls in the program; it can be reset by
|
|
reading all the elements from the hash, or by evaluating C<keys HASH> or
|
|
C<values HASH>. If you add or delete elements of a hash while you're
|
|
iterating over it, you may get entries skipped or duplicated, so don't.
|
|
|
|
The following prints out your environment like the printenv(1) program,
|
|
only in a different order:
|
|
|
|
while (($key,$value) = each %ENV) {
|
|
print "$key=$value\n";
|
|
}
|
|
|
|
See also C<keys()>, C<values()> and C<sort()>.
|
|
|
|
=item eof FILEHANDLE
|
|
|
|
=item eof ()
|
|
|
|
=item eof
|
|
|
|
Returns 1 if the next read on FILEHANDLE will return end of file, or if
|
|
FILEHANDLE is not open. FILEHANDLE may be an expression whose value
|
|
gives the real filehandle. (Note that this function actually
|
|
reads a character and then C<ungetc()>s it, so isn't very useful in an
|
|
interactive context.) Do not read from a terminal file (or call
|
|
C<eof(FILEHANDLE)> on it) after end-of-file is reached. Filetypes such
|
|
as terminals may lose the end-of-file condition if you do.
|
|
|
|
An C<eof> without an argument uses the last file read as argument.
|
|
Using C<eof()> with empty parentheses is very different. It indicates
|
|
the pseudo file formed of the files listed on the command line, i.e.,
|
|
C<eof()> is reasonable to use inside a C<while (E<lt>E<gt>)> loop to
|
|
detect the end of only the last file. Use C<eof(ARGV)> or eof without the
|
|
parentheses to test I<EACH> file in a while (E<lt>E<gt>) loop. Examples:
|
|
|
|
# reset line numbering on each input file
|
|
while (<>) {
|
|
next if /^\s*#/; # skip comments
|
|
print "$.\t$_";
|
|
} continue {
|
|
close ARGV if eof; # Not eof()!
|
|
}
|
|
|
|
# insert dashes just before last line of last file
|
|
while (<>) {
|
|
if (eof()) { # check for end of current file
|
|
print "--------------\n";
|
|
close(ARGV); # close or last; is needed if we
|
|
# are reading from the terminal
|
|
}
|
|
print;
|
|
}
|
|
|
|
Practical hint: you almost never need to use C<eof> in Perl, because the
|
|
input operators return false values when they run out of data, or if there
|
|
was an error.
|
|
|
|
=item eval EXPR
|
|
|
|
=item eval BLOCK
|
|
|
|
In the first form, the return value of EXPR is parsed and executed as if it
|
|
were a little Perl program. The value of the expression (which is itself
|
|
determined within scalar context) is first parsed, and if there weren't any
|
|
errors, executed in the context of the current Perl program, so that any
|
|
variable settings or subroutine and format definitions remain afterwards.
|
|
Note that the value is parsed every time the eval executes. If EXPR is
|
|
omitted, evaluates C<$_>. This form is typically used to delay parsing
|
|
and subsequent execution of the text of EXPR until run time.
|
|
|
|
In the second form, the code within the BLOCK is parsed only once--at the
|
|
same time the code surrounding the eval itself was parsed--and executed
|
|
within the context of the current Perl program. This form is typically
|
|
used to trap exceptions more efficiently than the first (see below), while
|
|
also providing the benefit of checking the code within BLOCK at compile
|
|
time.
|
|
|
|
The final semicolon, if any, may be omitted from the value of EXPR or within
|
|
the BLOCK.
|
|
|
|
In both forms, the value returned is the value of the last expression
|
|
evaluated inside the mini-program; a return statement may be also used, just
|
|
as with subroutines. The expression providing the return value is evaluated
|
|
in void, scalar, or list context, depending on the context of the eval itself.
|
|
See L</wantarray> for more on how the evaluation context can be determined.
|
|
|
|
If there is a syntax error or runtime error, or a C<die()> statement is
|
|
executed, an undefined value is returned by C<eval()>, and C<$@> is set to the
|
|
error message. If there was no error, C<$@> is guaranteed to be a null
|
|
string. Beware that using C<eval()> neither silences perl from printing
|
|
warnings to STDERR, nor does it stuff the text of warning messages into C<$@>.
|
|
To do either of those, you have to use the C<$SIG{__WARN__}> facility. See
|
|
L</warn> and L<perlvar>.
|
|
|
|
Note that, because C<eval()> traps otherwise-fatal errors, it is useful for
|
|
determining whether a particular feature (such as C<socket()> or C<symlink()>)
|
|
is implemented. It is also Perl's exception trapping mechanism, where
|
|
the die operator is used to raise exceptions.
|
|
|
|
If the code to be executed doesn't vary, you may use the eval-BLOCK
|
|
form to trap run-time errors without incurring the penalty of
|
|
recompiling each time. The error, if any, is still returned in C<$@>.
|
|
Examples:
|
|
|
|
# make divide-by-zero nonfatal
|
|
eval { $answer = $a / $b; }; warn $@ if $@;
|
|
|
|
# same thing, but less efficient
|
|
eval '$answer = $a / $b'; warn $@ if $@;
|
|
|
|
# a compile-time error
|
|
eval { $answer = }; # WRONG
|
|
|
|
# a run-time error
|
|
eval '$answer ='; # sets $@
|
|
|
|
Due to the current arguably broken state of C<__DIE__> hooks, when using
|
|
the C<eval{}> form as an exception trap in libraries, you may wish not
|
|
to trigger any C<__DIE__> hooks that user code may have installed.
|
|
You can use the C<local $SIG{__DIE__}> construct for this purpose,
|
|
as shown in this example:
|
|
|
|
# a very private exception trap for divide-by-zero
|
|
eval { local $SIG{'__DIE__'}; $answer = $a / $b; };
|
|
warn $@ if $@;
|
|
|
|
This is especially significant, given that C<__DIE__> hooks can call
|
|
C<die()> again, which has the effect of changing their error messages:
|
|
|
|
# __DIE__ hooks may modify error messages
|
|
{
|
|
local $SIG{'__DIE__'} =
|
|
sub { (my $x = $_[0]) =~ s/foo/bar/g; die $x };
|
|
eval { die "foo lives here" };
|
|
print $@ if $@; # prints "bar lives here"
|
|
}
|
|
|
|
Because this promotes action at a distance, this counterintuive behavior
|
|
may be fixed in a future release.
|
|
|
|
With an C<eval()>, you should be especially careful to remember what's
|
|
being looked at when:
|
|
|
|
eval $x; # CASE 1
|
|
eval "$x"; # CASE 2
|
|
|
|
eval '$x'; # CASE 3
|
|
eval { $x }; # CASE 4
|
|
|
|
eval "\$$x++"; # CASE 5
|
|
$$x++; # CASE 6
|
|
|
|
Cases 1 and 2 above behave identically: they run the code contained in
|
|
the variable C<$x>. (Although case 2 has misleading double quotes making
|
|
the reader wonder what else might be happening (nothing is).) Cases 3
|
|
and 4 likewise behave in the same way: they run the code C<'$x'>, which
|
|
does nothing but return the value of C<$x>. (Case 4 is preferred for
|
|
purely visual reasons, but it also has the advantage of compiling at
|
|
compile-time instead of at run-time.) Case 5 is a place where
|
|
normally you I<WOULD> like to use double quotes, except that in this
|
|
particular situation, you can just use symbolic references instead, as
|
|
in case 6.
|
|
|
|
C<eval BLOCK> does I<not> count as a loop, so the loop control statements
|
|
C<next>, C<last>, or C<redo> cannot be used to leave or restart the block.
|
|
|
|
=item exec LIST
|
|
|
|
=item exec PROGRAM LIST
|
|
|
|
The C<exec()> function executes a system command I<AND NEVER RETURNS> -
|
|
use C<system()> instead of C<exec()> if you want it to return. It fails and
|
|
returns FALSE only if the command does not exist I<and> it is executed
|
|
directly instead of via your system's command shell (see below).
|
|
|
|
Since it's a common mistake to use C<exec()> instead of C<system()>, Perl
|
|
warns you if there is a following statement which isn't C<die()>, C<warn()>,
|
|
or C<exit()> (if C<-w> is set - but you always do that). If you
|
|
I<really> want to follow an C<exec()> with some other statement, you
|
|
can use one of these styles to avoid the warning:
|
|
|
|
exec ('foo') or print STDERR "couldn't exec foo: $!";
|
|
{ exec ('foo') }; print STDERR "couldn't exec foo: $!";
|
|
|
|
If there is more than one argument in LIST, or if LIST is an array
|
|
with more than one value, calls execvp(3) with the arguments in LIST.
|
|
If there is only one scalar argument or an array with one element in it,
|
|
the argument is checked for shell metacharacters, and if there are any,
|
|
the entire argument is passed to the system's command shell for parsing
|
|
(this is C</bin/sh -c> on Unix platforms, but varies on other platforms).
|
|
If there are no shell metacharacters in the argument, it is split into
|
|
words and passed directly to C<execvp()>, which is more efficient. Note:
|
|
C<exec()> and C<system()> do not flush your output buffer, so you may need to
|
|
set C<$|> to avoid lost output. Examples:
|
|
|
|
exec '/bin/echo', 'Your arguments are: ', @ARGV;
|
|
exec "sort $outfile | uniq";
|
|
|
|
If you don't really want to execute the first argument, but want to lie
|
|
to the program you are executing about its own name, you can specify
|
|
the program you actually want to run as an "indirect object" (without a
|
|
comma) in front of the LIST. (This always forces interpretation of the
|
|
LIST as a multivalued list, even if there is only a single scalar in
|
|
the list.) Example:
|
|
|
|
$shell = '/bin/csh';
|
|
exec $shell '-sh'; # pretend it's a login shell
|
|
|
|
or, more directly,
|
|
|
|
exec {'/bin/csh'} '-sh'; # pretend it's a login shell
|
|
|
|
When the arguments get executed via the system shell, results will
|
|
be subject to its quirks and capabilities. See L<perlop/"`STRING`">
|
|
for details.
|
|
|
|
Using an indirect object with C<exec()> or C<system()> is also more secure.
|
|
This usage forces interpretation of the arguments as a multivalued list,
|
|
even if the list had just one argument. That way you're safe from the
|
|
shell expanding wildcards or splitting up words with whitespace in them.
|
|
|
|
@args = ( "echo surprise" );
|
|
|
|
exec @args; # subject to shell escapes
|
|
# if @args == 1
|
|
exec { $args[0] } @args; # safe even with one-arg list
|
|
|
|
The first version, the one without the indirect object, ran the I<echo>
|
|
program, passing it C<"surprise"> an argument. The second version
|
|
didn't--it tried to run a program literally called I<"echo surprise">,
|
|
didn't find it, and set C<$?> to a non-zero value indicating failure.
|
|
|
|
Note that C<exec()> will not call your C<END> blocks, nor will it call
|
|
any C<DESTROY> methods in your objects.
|
|
|
|
=item exists EXPR
|
|
|
|
Returns TRUE if the specified hash key exists in its hash array, even
|
|
if the corresponding value is undefined.
|
|
|
|
print "Exists\n" if exists $array{$key};
|
|
print "Defined\n" if defined $array{$key};
|
|
print "True\n" if $array{$key};
|
|
|
|
A hash element can be TRUE only if it's defined, and defined if
|
|
it exists, but the reverse doesn't necessarily hold true.
|
|
|
|
Note that the EXPR can be arbitrarily complicated as long as the final
|
|
operation is a hash key lookup:
|
|
|
|
if (exists $ref->{A}->{B}->{$key}) { }
|
|
if (exists $hash{A}{B}{$key}) { }
|
|
|
|
Although the last element will not spring into existence just because
|
|
its existence was tested, intervening ones will. Thus C<$ref-E<gt>{"A"}>
|
|
and C<$ref-E<gt>{"A"}-E<gt>{"B"}> will spring into existence due to the
|
|
existence test for a $key element. This happens anywhere the arrow
|
|
operator is used, including even
|
|
|
|
undef $ref;
|
|
if (exists $ref->{"Some key"}) { }
|
|
print $ref; # prints HASH(0x80d3d5c)
|
|
|
|
This surprising autovivification in what does not at first--or even
|
|
second--glance appear to be an lvalue context may be fixed in a future
|
|
release.
|
|
|
|
=item exit EXPR
|
|
|
|
Evaluates EXPR and exits immediately with that value. Example:
|
|
|
|
$ans = <STDIN>;
|
|
exit 0 if $ans =~ /^[Xx]/;
|
|
|
|
See also C<die()>. If EXPR is omitted, exits with C<0> status. The only
|
|
universally recognized values for EXPR are C<0> for success and C<1>
|
|
for error; other values are subject to interpretation depending on the
|
|
environment in which the Perl program is running. For example, exiting
|
|
69 (EX_UNAVAILABLE) from a I<sendmail> incoming-mail filter will cause
|
|
the mailer to return the item undelivered, but that's not true everywhere.
|
|
|
|
Don't use C<exit()> to abort a subroutine if there's any chance that
|
|
someone might want to trap whatever error happened. Use C<die()> instead,
|
|
which can be trapped by an C<eval()>.
|
|
|
|
The exit() function does not always exit immediately. It calls any
|
|
defined C<END> routines first, but these C<END> routines may not
|
|
themselves abort the exit. Likewise any object destructors that need to
|
|
be called are called before the real exit. If this is a problem, you
|
|
can call C<POSIX:_exit($status)> to avoid END and destructor processing.
|
|
See L<perlsub> for details.
|
|
|
|
=item exp EXPR
|
|
|
|
=item exp
|
|
|
|
Returns I<e> (the natural logarithm base) to the power of EXPR.
|
|
If EXPR is omitted, gives C<exp($_)>.
|
|
|
|
=item fcntl FILEHANDLE,FUNCTION,SCALAR
|
|
|
|
Implements the fcntl(2) function. You'll probably have to say
|
|
|
|
use Fcntl;
|
|
|
|
first to get the correct constant definitions. Argument processing and
|
|
value return works just like C<ioctl()> below.
|
|
For example:
|
|
|
|
use Fcntl;
|
|
fcntl($filehandle, F_GETFL, $packed_return_buffer)
|
|
or die "can't fcntl F_GETFL: $!";
|
|
|
|
You don't have to check for C<defined()> on the return from C<fnctl()>.
|
|
Like C<ioctl()>, it maps a C<0> return from the system call into "C<0>
|
|
but true" in Perl. This string is true in boolean context and C<0>
|
|
in numeric context. It is also exempt from the normal B<-w> warnings
|
|
on improper numeric conversions.
|
|
|
|
Note that C<fcntl()> will produce a fatal error if used on a machine that
|
|
doesn't implement fcntl(2). See the Fcntl module or your fcntl(2)
|
|
manpage to learn what functions are available on your system.
|
|
|
|
=item fileno FILEHANDLE
|
|
|
|
Returns the file descriptor for a filehandle, or undefined if the
|
|
filehandle is not open. This is mainly useful for constructing
|
|
bitmaps for C<select()> and low-level POSIX tty-handling operations.
|
|
If FILEHANDLE is an expression, the value is taken as an indirect
|
|
filehandle, generally its name.
|
|
|
|
You can use this to find out whether two handles refer to the
|
|
same underlying descriptor:
|
|
|
|
if (fileno(THIS) == fileno(THAT)) {
|
|
print "THIS and THAT are dups\n";
|
|
}
|
|
|
|
=item flock FILEHANDLE,OPERATION
|
|
|
|
Calls flock(2), or an emulation of it, on FILEHANDLE. Returns TRUE
|
|
for success, FALSE on failure. Produces a fatal error if used on a
|
|
machine that doesn't implement flock(2), fcntl(2) locking, or lockf(3).
|
|
C<flock()> is Perl's portable file locking interface, although it locks
|
|
only entire files, not records.
|
|
|
|
Two potentially non-obvious but traditional C<flock> semantics are
|
|
that it waits indefinitely until the lock is granted, and that its locks
|
|
B<merely advisory>. Such discretionary locks are more flexible, but offer
|
|
fewer guarantees. This means that files locked with C<flock()> may be
|
|
modified by programs that do not also use C<flock()>. See L<perlport>,
|
|
your port's specific documentation, or your system-specific local manpages
|
|
for details. It's best to assume traditional behavior if you're writing
|
|
portable programs. (But if you're not, you should as always feel perfectly
|
|
free to write for your own system's idiosyncrasies (sometimes called
|
|
"features"). Slavish adherence to portability concerns shouldn't get
|
|
in the way of your getting your job done.)
|
|
|
|
OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN, possibly combined with
|
|
LOCK_NB. These constants are traditionally valued 1, 2, 8 and 4, but
|
|
you can use the symbolic names if import them from the Fcntl module,
|
|
either individually, or as a group using the ':flock' tag. LOCK_SH
|
|
requests a shared lock, LOCK_EX requests an exclusive lock, and LOCK_UN
|
|
releases a previously requested lock. If LOCK_NB is added to LOCK_SH or
|
|
LOCK_EX then C<flock()> will return immediately rather than blocking
|
|
waiting for the lock (check the return status to see if you got it).
|
|
|
|
To avoid the possibility of miscoordination, Perl now flushes FILEHANDLE
|
|
before locking or unlocking it.
|
|
|
|
Note that the emulation built with lockf(3) doesn't provide shared
|
|
locks, and it requires that FILEHANDLE be open with write intent. These
|
|
are the semantics that lockf(3) implements. Most if not all systems
|
|
implement lockf(3) in terms of fcntl(2) locking, though, so the
|
|
differing semantics shouldn't bite too many people.
|
|
|
|
Note also that some versions of C<flock()> cannot lock things over the
|
|
network; you would need to use the more system-specific C<fcntl()> for
|
|
that. If you like you can force Perl to ignore your system's flock(2)
|
|
function, and so provide its own fcntl(2)-based emulation, by passing
|
|
the switch C<-Ud_flock> to the F<Configure> program when you configure
|
|
perl.
|
|
|
|
Here's a mailbox appender for BSD systems.
|
|
|
|
use Fcntl ':flock'; # import LOCK_* constants
|
|
|
|
sub lock {
|
|
flock(MBOX,LOCK_EX);
|
|
# and, in case someone appended
|
|
# while we were waiting...
|
|
seek(MBOX, 0, 2);
|
|
}
|
|
|
|
sub unlock {
|
|
flock(MBOX,LOCK_UN);
|
|
}
|
|
|
|
open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}")
|
|
or die "Can't open mailbox: $!";
|
|
|
|
lock();
|
|
print MBOX $msg,"\n\n";
|
|
unlock();
|
|
|
|
On systems that support a real flock(), locks are inherited across fork()
|
|
calls, whereas those that must resort to the more capricious fcntl()
|
|
function lose the locks, making it harder to write servers.
|
|
|
|
See also L<DB_File> for other flock() examples.
|
|
|
|
=item fork
|
|
|
|
Does a fork(2) system call to create a new process running the
|
|
same program at the same point. It returns the child pid to the
|
|
parent process, C<0> to the child process, or C<undef> if the fork is
|
|
unsuccessful. File descriptors (and sometimes locks on those descriptors)
|
|
are shared, while everything else is copied. On most systems supporting
|
|
fork(), great care has gone into making it extremely efficient (for
|
|
example, using copy-on-write technology on data pages), making it the
|
|
dominant paradigm for multitasking over the last few decades.
|
|
|
|
Note: unflushed buffers remain unflushed in both processes, which means
|
|
you may need to set C<$|> ($AUTOFLUSH in English) or call the C<autoflush()>
|
|
method of C<IO::Handle> to avoid duplicate output.
|
|
|
|
If you C<fork()> without ever waiting on your children, you will
|
|
accumulate zombies. On some systems, you can avoid this by setting
|
|
C<$SIG{CHLD}> to C<"IGNORE">. See also L<perlipc> for more examples of
|
|
forking and reaping moribund children.
|
|
|
|
Note that if your forked child inherits system file descriptors like
|
|
STDIN and STDOUT that are actually connected by a pipe or socket, even
|
|
if you exit, then the remote server (such as, say, a CGI script or a
|
|
backgrounded job launced from a remote shell) won't think you're done.
|
|
You should reopen those to F</dev/null> if it's any issue.
|
|
|
|
=item format
|
|
|
|
Declare a picture format for use by the C<write()> function. For
|
|
example:
|
|
|
|
format Something =
|
|
Test: @<<<<<<<< @||||| @>>>>>
|
|
$str, $%, '$' . int($num)
|
|
.
|
|
|
|
$str = "widget";
|
|
$num = $cost/$quantity;
|
|
$~ = 'Something';
|
|
write;
|
|
|
|
See L<perlform> for many details and examples.
|
|
|
|
=item formline PICTURE,LIST
|
|
|
|
This is an internal function used by C<format>s, though you may call it,
|
|
too. It formats (see L<perlform>) a list of values according to the
|
|
contents of PICTURE, placing the output into the format output
|
|
accumulator, C<$^A> (or C<$ACCUMULATOR> in English).
|
|
Eventually, when a C<write()> is done, the contents of
|
|
C<$^A> are written to some filehandle, but you could also read C<$^A>
|
|
yourself and then set C<$^A> back to C<"">. Note that a format typically
|
|
does one C<formline()> per line of form, but the C<formline()> function itself
|
|
doesn't care how many newlines are embedded in the PICTURE. This means
|
|
that the C<~> and C<~~> tokens will treat the entire PICTURE as a single line.
|
|
You may therefore need to use multiple formlines to implement a single
|
|
record format, just like the format compiler.
|
|
|
|
Be careful if you put double quotes around the picture, because an "C<@>"
|
|
character may be taken to mean the beginning of an array name.
|
|
C<formline()> always returns TRUE. See L<perlform> for other examples.
|
|
|
|
=item getc FILEHANDLE
|
|
|
|
=item getc
|
|
|
|
Returns the next character from the input file attached to FILEHANDLE,
|
|
or the undefined value at end of file, or if there was an error.
|
|
If FILEHANDLE is omitted, reads from STDIN. This is not particularly
|
|
efficient. However, it cannot be used by itself to fetch single
|
|
characters without waiting for the user to hit enter. For that, try
|
|
something more like:
|
|
|
|
if ($BSD_STYLE) {
|
|
system "stty cbreak </dev/tty >/dev/tty 2>&1";
|
|
}
|
|
else {
|
|
system "stty", '-icanon', 'eol', "\001";
|
|
}
|
|
|
|
$key = getc(STDIN);
|
|
|
|
if ($BSD_STYLE) {
|
|
system "stty -cbreak </dev/tty >/dev/tty 2>&1";
|
|
}
|
|
else {
|
|
system "stty", 'icanon', 'eol', '^@'; # ASCII null
|
|
}
|
|
print "\n";
|
|
|
|
Determination of whether $BSD_STYLE should be set
|
|
is left as an exercise to the reader.
|
|
|
|
The C<POSIX::getattr()> function can do this more portably on
|
|
systems purporting POSIX compliance. See also the C<Term::ReadKey>
|
|
module from your nearest CPAN site; details on CPAN can be found on
|
|
L<perlmodlib/CPAN>.
|
|
|
|
=item getlogin
|
|
|
|
Implements the C library function of the same name, which on most
|
|
systems returns the current login from F</etc/utmp>, if any. If null,
|
|
use C<getpwuid()>.
|
|
|
|
$login = getlogin || getpwuid($<) || "Kilroy";
|
|
|
|
Do not consider C<getlogin()> for authentication: it is not as
|
|
secure as C<getpwuid()>.
|
|
|
|
=item getpeername SOCKET
|
|
|
|
Returns the packed sockaddr address of other end of the SOCKET connection.
|
|
|
|
use Socket;
|
|
$hersockaddr = getpeername(SOCK);
|
|
($port, $iaddr) = unpack_sockaddr_in($hersockaddr);
|
|
$herhostname = gethostbyaddr($iaddr, AF_INET);
|
|
$herstraddr = inet_ntoa($iaddr);
|
|
|
|
=item getpgrp PID
|
|
|
|
Returns the current process group for the specified PID. Use
|
|
a PID of C<0> to get the current process group for the
|
|
current process. Will raise an exception if used on a machine that
|
|
doesn't implement getpgrp(2). If PID is omitted, returns process
|
|
group of current process. Note that the POSIX version of C<getpgrp()>
|
|
does not accept a PID argument, so only C<PID==0> is truly portable.
|
|
|
|
=item getppid
|
|
|
|
Returns the process id of the parent process.
|
|
|
|
=item getpriority WHICH,WHO
|
|
|
|
Returns the current priority for a process, a process group, or a user.
|
|
(See L<getpriority(2)>.) Will raise a fatal exception if used on a
|
|
machine that doesn't implement getpriority(2).
|
|
|
|
=item getpwnam NAME
|
|
|
|
=item getgrnam NAME
|
|
|
|
=item gethostbyname NAME
|
|
|
|
=item getnetbyname NAME
|
|
|
|
=item getprotobyname NAME
|
|
|
|
=item getpwuid UID
|
|
|
|
=item getgrgid GID
|
|
|
|
=item getservbyname NAME,PROTO
|
|
|
|
=item gethostbyaddr ADDR,ADDRTYPE
|
|
|
|
=item getnetbyaddr ADDR,ADDRTYPE
|
|
|
|
=item getprotobynumber NUMBER
|
|
|
|
=item getservbyport PORT,PROTO
|
|
|
|
=item getpwent
|
|
|
|
=item getgrent
|
|
|
|
=item gethostent
|
|
|
|
=item getnetent
|
|
|
|
=item getprotoent
|
|
|
|
=item getservent
|
|
|
|
=item setpwent
|
|
|
|
=item setgrent
|
|
|
|
=item sethostent STAYOPEN
|
|
|
|
=item setnetent STAYOPEN
|
|
|
|
=item setprotoent STAYOPEN
|
|
|
|
=item setservent STAYOPEN
|
|
|
|
=item endpwent
|
|
|
|
=item endgrent
|
|
|
|
=item endhostent
|
|
|
|
=item endnetent
|
|
|
|
=item endprotoent
|
|
|
|
=item endservent
|
|
|
|
These routines perform the same functions as their counterparts in the
|
|
system library. In list context, the return values from the
|
|
various get routines are as follows:
|
|
|
|
($name,$passwd,$uid,$gid,
|
|
$quota,$comment,$gcos,$dir,$shell,$expire) = getpw*
|
|
($name,$passwd,$gid,$members) = getgr*
|
|
($name,$aliases,$addrtype,$length,@addrs) = gethost*
|
|
($name,$aliases,$addrtype,$net) = getnet*
|
|
($name,$aliases,$proto) = getproto*
|
|
($name,$aliases,$port,$proto) = getserv*
|
|
|
|
(If the entry doesn't exist you get a null list.)
|
|
|
|
In scalar context, you get the name, unless the function was a
|
|
lookup by name, in which case you get the other thing, whatever it is.
|
|
(If the entry doesn't exist you get the undefined value.) For example:
|
|
|
|
$uid = getpwnam($name);
|
|
$name = getpwuid($num);
|
|
$name = getpwent();
|
|
$gid = getgrnam($name);
|
|
$name = getgrgid($num;
|
|
$name = getgrent();
|
|
#etc.
|
|
|
|
In I<getpw*()> the fields C<$quota>, C<$comment>, and C<$expire> are
|
|
special cases in the sense that in many systems they are unsupported.
|
|
If the C<$quota> is unsupported, it is an empty scalar. If it is
|
|
supported, it usually encodes the disk quota. If the C<$comment>
|
|
field is unsupported, it is an empty scalar. If it is supported it
|
|
usually encodes some administrative comment about the user. In some
|
|
systems the $quota field may be C<$change> or C<$age>, fields that have
|
|
to do with password aging. In some systems the C<$comment> field may
|
|
be C<$class>. The C<$expire> field, if present, encodes the expiration
|
|
period of the account or the password. For the availability and the
|
|
exact meaning of these fields in your system, please consult your
|
|
getpwnam(3) documentation and your F<pwd.h> file. You can also find
|
|
out from within Perl what your C<$quota> and C<$comment> fields mean
|
|
and whether you have the C<$expire> field by using the C<Config> module
|
|
and the values C<d_pwquota>, C<d_pwage>, C<d_pwchange>, C<d_pwcomment>,
|
|
and C<d_pwexpire>. Shadow password files are only supported if your
|
|
vendor has implemented them in the intuitive fashion that calling the
|
|
regular C library routines gets the shadow versions if you're running
|
|
under privilege. Those that incorrectly implement a separate library
|
|
call are not supported.
|
|
|
|
The C<$members> value returned by I<getgr*()> is a space separated list of
|
|
the login names of the members of the group.
|
|
|
|
For the I<gethost*()> functions, if the C<h_errno> variable is supported in
|
|
C, it will be returned to you via C<$?> if the function call fails. The
|
|
C<@addrs> value returned by a successful call is a list of the raw
|
|
addresses returned by the corresponding system library call. In the
|
|
Internet domain, each address is four bytes long and you can unpack it
|
|
by saying something like:
|
|
|
|
($a,$b,$c,$d) = unpack('C4',$addr[0]);
|
|
|
|
The Socket library makes this slightly easier:
|
|
|
|
use Socket;
|
|
$iaddr = inet_aton("127.1"); # or whatever address
|
|
$name = gethostbyaddr($iaddr, AF_INET);
|
|
|
|
# or going the other way
|
|
$straddr = inet_ntoa($iaddr");
|
|
|
|
If you get tired of remembering which element of the return list contains
|
|
which return value, by-name interfaces are also provided in modules:
|
|
C<File::stat>, C<Net::hostent>, C<Net::netent>, C<Net::protoent>, C<Net::servent>,
|
|
C<Time::gmtime>, C<Time::localtime>, and C<User::grent>. These override the
|
|
normal built-in, replacing them with versions that return objects with
|
|
the appropriate names for each field. For example:
|
|
|
|
use File::stat;
|
|
use User::pwent;
|
|
$is_his = (stat($filename)->uid == pwent($whoever)->uid);
|
|
|
|
Even though it looks like they're the same method calls (uid),
|
|
they aren't, because a C<File::stat> object is different from a C<User::pwent> object.
|
|
|
|
=item getsockname SOCKET
|
|
|
|
Returns the packed sockaddr address of this end of the SOCKET connection.
|
|
|
|
use Socket;
|
|
$mysockaddr = getsockname(SOCK);
|
|
($port, $myaddr) = unpack_sockaddr_in($mysockaddr);
|
|
|
|
=item getsockopt SOCKET,LEVEL,OPTNAME
|
|
|
|
Returns the socket option requested, or undef if there is an error.
|
|
|
|
=item glob EXPR
|
|
|
|
=item glob
|
|
|
|
Returns the value of EXPR with filename expansions such as the
|
|
standard Unix shell F</bin/csh> would do. This is the internal function
|
|
implementing the C<E<lt>*.cE<gt>> operator, but you can use it directly.
|
|
If EXPR is omitted, C<$_> is used. The C<E<lt>*.cE<gt>> operator is
|
|
discussed in more detail in L<perlop/"I/O Operators">.
|
|
|
|
=item gmtime EXPR
|
|
|
|
Converts a time as returned by the time function to a 9-element array
|
|
with the time localized for the standard Greenwich time zone.
|
|
Typically used as follows:
|
|
|
|
# 0 1 2 3 4 5 6 7 8
|
|
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
|
|
gmtime(time);
|
|
|
|
All array elements are numeric, and come straight out of a struct tm.
|
|
In particular this means that C<$mon> has the range C<0..11> and C<$wday>
|
|
has the range C<0..6> with sunday as day C<0>. Also, C<$year> is the
|
|
number of years since 1900, that is, C<$year> is C<123> in year 2023,
|
|
I<not> simply the last two digits of the year. If you assume it is,
|
|
then you create non-Y2K-compliant programs--and you wouldn't want to do
|
|
that, would you?
|
|
|
|
If EXPR is omitted, does C<gmtime(time())>.
|
|
|
|
In scalar context, returns the ctime(3) value:
|
|
|
|
$now_string = gmtime; # e.g., "Thu Oct 13 04:54:34 1994"
|
|
|
|
Also see the C<timegm()> function provided by the C<Time::Local> module,
|
|
and the strftime(3) function available via the POSIX module.
|
|
|
|
This scalar value is B<not> locale dependent (see L<perllocale>), but
|
|
is instead a Perl builtin. Also see the C<Time::Local> module, and the
|
|
strftime(3) and mktime(3) functions available via the POSIX module. To
|
|
get somewhat similar but locale dependent date strings, set up your
|
|
locale environment variables appropriately (please see L<perllocale>)
|
|
and try for example:
|
|
|
|
use POSIX qw(strftime);
|
|
$now_string = strftime "%a %b %e %H:%M:%S %Y", gmtime;
|
|
|
|
Note that the C<%a> and C<%b> escapes, which represent the short forms
|
|
of the day of the week and the month of the year, may not necessarily
|
|
be three characters wide in all locales.
|
|
|
|
=item goto LABEL
|
|
|
|
=item goto EXPR
|
|
|
|
=item goto &NAME
|
|
|
|
The C<goto-LABEL> form finds the statement labeled with LABEL and resumes
|
|
execution there. It may not be used to go into any construct that
|
|
requires initialization, such as a subroutine or a C<foreach> loop. It
|
|
also can't be used to go into a construct that is optimized away,
|
|
or to get out of a block or subroutine given to C<sort()>.
|
|
It can be used to go almost anywhere else within the dynamic scope,
|
|
including out of subroutines, but it's usually better to use some other
|
|
construct such as C<last> or C<die()>. The author of Perl has never felt the
|
|
need to use this form of C<goto> (in Perl, that is--C is another matter).
|
|
|
|
The C<goto-EXPR> form expects a label name, whose scope will be resolved
|
|
dynamically. This allows for computed C<goto>s per FORTRAN, but isn't
|
|
necessarily recommended if you're optimizing for maintainability:
|
|
|
|
goto ("FOO", "BAR", "GLARCH")[$i];
|
|
|
|
The C<goto-&NAME> form is highly magical, and substitutes a call to the
|
|
named subroutine for the currently running subroutine. This is used by
|
|
C<AUTOLOAD> subroutines that wish to load another subroutine and then
|
|
pretend that the other subroutine had been called in the first place
|
|
(except that any modifications to C<@_> in the current subroutine are
|
|
propagated to the other subroutine.) After the C<goto>, not even C<caller()>
|
|
will be able to tell that this routine was called first.
|
|
|
|
=item grep BLOCK LIST
|
|
|
|
=item grep EXPR,LIST
|
|
|
|
This is similar in spirit to, but not the same as, grep(1) and its
|
|
relatives. In particular, it is not limited to using regular expressions.
|
|
|
|
Evaluates the BLOCK or EXPR for each element of LIST (locally setting
|
|
C<$_> to each element) and returns the list value consisting of those
|
|
elements for which the expression evaluated to TRUE. In scalar
|
|
context, returns the number of times the expression was TRUE.
|
|
|
|
@foo = grep(!/^#/, @bar); # weed out comments
|
|
|
|
or equivalently,
|
|
|
|
@foo = grep {!/^#/} @bar; # weed out comments
|
|
|
|
Note that, because C<$_> is a reference into the list value, it can
|
|
be used to modify the elements of the array. While this is useful and
|
|
supported, it can cause bizarre results if the LIST is not a named array.
|
|
Similarly, grep returns aliases into the original list, much as a for
|
|
loop's index variable aliases the list elements. That is, modifying an
|
|
element of a list returned by grep (for example, in a C<foreach>, C<map()>
|
|
or another C<grep()>) actually modifies the element in the original list.
|
|
This is usually something to be avoided when writing clear code.
|
|
|
|
See also L</map> for an array composed of the results of the BLOCK or EXPR.
|
|
|
|
=item hex EXPR
|
|
|
|
=item hex
|
|
|
|
Interprets EXPR as a hex string and returns the corresponding value.
|
|
(To convert strings that might start with either 0, 0x, or 0b, see
|
|
L</oct>.) If EXPR is omitted, uses C<$_>.
|
|
|
|
print hex '0xAf'; # prints '175'
|
|
print hex 'aF'; # same
|
|
|
|
=item import
|
|
|
|
There is no builtin C<import()> function. It is just an ordinary
|
|
method (subroutine) defined (or inherited) by modules that wish to export
|
|
names to another module. The C<use()> function calls the C<import()> method
|
|
for the package used. See also L</use()>, L<perlmod>, and L<Exporter>.
|
|
|
|
=item index STR,SUBSTR,POSITION
|
|
|
|
=item index STR,SUBSTR
|
|
|
|
The index function searches for one string within another, but without
|
|
the wildcard-like behavior of a full regular-expression pattern match.
|
|
It returns the position of the first occurrence of SUBSTR in STR at
|
|
or after POSITION. If POSITION is omitted, starts searching from the
|
|
beginning of the string. The return value is based at C<0> (or whatever
|
|
you've set the C<$[> variable to--but don't do that). If the substring
|
|
is not found, returns one less than the base, ordinarily C<-1>.
|
|
|
|
=item int EXPR
|
|
|
|
=item int
|
|
|
|
Returns the integer portion of EXPR. If EXPR is omitted, uses C<$_>.
|
|
You should not use this function for rounding: one because it truncates
|
|
towards C<0>, and two because machine representations of floating point
|
|
numbers can sometimes produce counterintuitive results. For example,
|
|
C<int(-6.725/0.025)> produces -268 rather than the correct -269; that's
|
|
because it's really more like -268.99999999999994315658 instead. Usually,
|
|
the C<sprintf()>, C<printf()>, or the C<POSIX::floor> and C<POSIX::ceil>
|
|
functions will serve you better than will int().
|
|
|
|
=item ioctl FILEHANDLE,FUNCTION,SCALAR
|
|
|
|
Implements the ioctl(2) function. You'll probably first have to say
|
|
|
|
require "ioctl.ph"; # probably in /usr/local/lib/perl/ioctl.ph
|
|
|
|
to get the correct function definitions. If F<ioctl.ph> doesn't
|
|
exist or doesn't have the correct definitions you'll have to roll your
|
|
own, based on your C header files such as F<E<lt>sys/ioctl.hE<gt>>.
|
|
(There is a Perl script called B<h2ph> that comes with the Perl kit that
|
|
may help you in this, but it's nontrivial.) SCALAR will be read and/or
|
|
written depending on the FUNCTION--a pointer to the string value of SCALAR
|
|
will be passed as the third argument of the actual C<ioctl()> call. (If SCALAR
|
|
has no string value but does have a numeric value, that value will be
|
|
passed rather than a pointer to the string value. To guarantee this to be
|
|
TRUE, add a C<0> to the scalar before using it.) The C<pack()> and C<unpack()>
|
|
functions are useful for manipulating the values of structures used by
|
|
C<ioctl()>. The following example sets the erase character to DEL.
|
|
|
|
require 'ioctl.ph';
|
|
$getp = &TIOCGETP;
|
|
die "NO TIOCGETP" if $@ || !$getp;
|
|
$sgttyb_t = "ccccs"; # 4 chars and a short
|
|
if (ioctl(STDIN,$getp,$sgttyb)) {
|
|
@ary = unpack($sgttyb_t,$sgttyb);
|
|
$ary[2] = 127;
|
|
$sgttyb = pack($sgttyb_t,@ary);
|
|
ioctl(STDIN,&TIOCSETP,$sgttyb)
|
|
|| die "Can't ioctl: $!";
|
|
}
|
|
|
|
The return value of C<ioctl()> (and C<fcntl()>) is as follows:
|
|
|
|
if OS returns: then Perl returns:
|
|
-1 undefined value
|
|
0 string "0 but true"
|
|
anything else that number
|
|
|
|
Thus Perl returns TRUE on success and FALSE on failure, yet you can
|
|
still easily determine the actual value returned by the operating
|
|
system:
|
|
|
|
$retval = ioctl(...) || -1;
|
|
printf "System returned %d\n", $retval;
|
|
|
|
The special string "C<0> but true" is exempt from B<-w> complaints
|
|
about improper numeric conversions.
|
|
|
|
=item join EXPR,LIST
|
|
|
|
Joins the separate strings of LIST into a single string with fields
|
|
separated by the value of EXPR, and returns that new string. Example:
|
|
|
|
$rec = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell);
|
|
|
|
See L</split>.
|
|
|
|
=item keys HASH
|
|
|
|
Returns a list consisting of all the keys of the named hash. (In a
|
|
scalar context, returns the number of keys.) The keys are returned in
|
|
an apparently random order. The actual random order is subject to
|
|
change in future versions of perl, but it is guaranteed to be the same
|
|
order as either the C<values()> or C<each()> function produces (given
|
|
that the hash has not been modified). As a side effect, it resets
|
|
HASH's iterator.
|
|
|
|
Here is yet another way to print your environment:
|
|
|
|
@keys = keys %ENV;
|
|
@values = values %ENV;
|
|
while ($#keys >= 0) {
|
|
print pop(@keys), '=', pop(@values), "\n";
|
|
}
|
|
|
|
or how about sorted by key:
|
|
|
|
foreach $key (sort(keys %ENV)) {
|
|
print $key, '=', $ENV{$key}, "\n";
|
|
}
|
|
|
|
To sort a hash by value, you'll need to use a C<sort()> function.
|
|
Here's a descending numeric sort of a hash by its values:
|
|
|
|
foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash) {
|
|
printf "%4d %s\n", $hash{$key}, $key;
|
|
}
|
|
|
|
As an lvalue C<keys()> allows you to increase the number of hash buckets
|
|
allocated for the given hash. This can gain you a measure of efficiency if
|
|
you know the hash is going to get big. (This is similar to pre-extending
|
|
an array by assigning a larger number to $#array.) If you say
|
|
|
|
keys %hash = 200;
|
|
|
|
then C<%hash> will have at least 200 buckets allocated for it--256 of them,
|
|
in fact, since it rounds up to the next power of two. These
|
|
buckets will be retained even if you do C<%hash = ()>, use C<undef
|
|
%hash> if you want to free the storage while C<%hash> is still in scope.
|
|
You can't shrink the number of buckets allocated for the hash using
|
|
C<keys()> in this way (but you needn't worry about doing this by accident,
|
|
as trying has no effect).
|
|
|
|
See also C<each()>, C<values()> and C<sort()>.
|
|
|
|
=item kill LIST
|
|
|
|
Sends a signal to a list of processes. The first element of
|
|
the list must be the signal to send. Returns the number of
|
|
processes successfully signaled.
|
|
|
|
$cnt = kill 1, $child1, $child2;
|
|
kill 9, @goners;
|
|
|
|
Unlike in the shell, in Perl if the I<SIGNAL> is negative, it kills
|
|
process groups instead of processes. (On System V, a negative I<PROCESS>
|
|
number will also kill process groups, but that's not portable.) That
|
|
means you usually want to use positive not negative signals. You may also
|
|
use a signal name in quotes. See L<perlipc/"Signals"> for details.
|
|
|
|
=item last LABEL
|
|
|
|
=item last
|
|
|
|
The C<last> command is like the C<break> statement in C (as used in
|
|
loops); it immediately exits the loop in question. If the LABEL is
|
|
omitted, the command refers to the innermost enclosing loop. The
|
|
C<continue> block, if any, is not executed:
|
|
|
|
LINE: while (<STDIN>) {
|
|
last LINE if /^$/; # exit when done with header
|
|
#...
|
|
}
|
|
|
|
C<last> cannot be used to exit a block which returns a value such as
|
|
C<eval {}>, C<sub {}> or C<do {}>, and should not be used to exit
|
|
a grep() or map() operation.
|
|
|
|
See also L</continue> for an illustration of how C<last>, C<next>, and
|
|
C<redo> work.
|
|
|
|
=item lc EXPR
|
|
|
|
=item lc
|
|
|
|
Returns an lowercased version of EXPR. This is the internal function
|
|
implementing the C<\L> escape in double-quoted strings.
|
|
Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>.
|
|
|
|
If EXPR is omitted, uses C<$_>.
|
|
|
|
=item lcfirst EXPR
|
|
|
|
=item lcfirst
|
|
|
|
Returns the value of EXPR with the first character lowercased. This is
|
|
the internal function implementing the C<\l> escape in double-quoted strings.
|
|
Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>.
|
|
|
|
If EXPR is omitted, uses C<$_>.
|
|
|
|
=item length EXPR
|
|
|
|
=item length
|
|
|
|
Returns the length in characters of the value of EXPR. If EXPR is
|
|
omitted, returns length of C<$_>. Note that this cannot be used on
|
|
an entire array or hash to find out how many elements these have.
|
|
For that, use C<scalar @array> and C<scalar keys %hash> respectively.
|
|
|
|
=item link OLDFILE,NEWFILE
|
|
|
|
Creates a new filename linked to the old filename. Returns TRUE for
|
|
success, FALSE otherwise.
|
|
|
|
=item listen SOCKET,QUEUESIZE
|
|
|
|
Does the same thing that the listen system call does. Returns TRUE if
|
|
it succeeded, FALSE otherwise. See the example in L<perlipc/"Sockets: Client/Server Communication">.
|
|
|
|
=item local EXPR
|
|
|
|
You really probably want to be using C<my()> instead, because C<local()> isn't
|
|
what most people think of as "local". See L<perlsub/"Private Variables
|
|
via my()"> for details.
|
|
|
|
A local modifies the listed variables to be local to the enclosing
|
|
block, file, or eval. If more than one value is listed, the list must
|
|
be placed in parentheses. See L<perlsub/"Temporary Values via local()">
|
|
for details, including issues with tied arrays and hashes.
|
|
|
|
=item localtime EXPR
|
|
|
|
Converts a time as returned by the time function to a 9-element array
|
|
with the time analyzed for the local time zone. Typically used as
|
|
follows:
|
|
|
|
# 0 1 2 3 4 5 6 7 8
|
|
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
|
|
localtime(time);
|
|
|
|
All array elements are numeric, and come straight out of a struct tm.
|
|
In particular this means that C<$mon> has the range C<0..11> and C<$wday>
|
|
has the range C<0..6> with sunday as day C<0>. Also, C<$year> is the
|
|
number of years since 1900, that is, C<$year> is C<123> in year 2023,
|
|
and I<not> simply the last two digits of the year. If you assume it is,
|
|
then you create non-Y2K-compliant programs--and you wouldn't want to do
|
|
that, would you?
|
|
|
|
If EXPR is omitted, uses the current time (C<localtime(time)>).
|
|
|
|
In scalar context, returns the ctime(3) value:
|
|
|
|
$now_string = localtime; # e.g., "Thu Oct 13 04:54:34 1994"
|
|
|
|
This scalar value is B<not> locale dependent, see L<perllocale>, but
|
|
instead a Perl builtin. Also see the C<Time::Local> module, and the
|
|
strftime(3) and mktime(3) function available via the POSIX module. To
|
|
get somewhat similar but locale dependent date strings, set up your
|
|
locale environment variables appropriately (please see L<perllocale>)
|
|
and try for example:
|
|
|
|
use POSIX qw(strftime);
|
|
$now_string = strftime "%a %b %e %H:%M:%S %Y", localtime;
|
|
|
|
Note that the C<%a> and C<%b>, the short forms of the day of the week
|
|
and the month of the year, may not necessarily be three characters wide.
|
|
|
|
=item log EXPR
|
|
|
|
=item log
|
|
|
|
Returns the natural logarithm (base I<e>) of EXPR. If EXPR is omitted,
|
|
returns log of C<$_>. To get the log of another base, use basic algebra:
|
|
The base-N log of a number is is equal to the natural log of that number
|
|
divided by the natural log of N. For example:
|
|
|
|
sub log10 {
|
|
my $n = shift;
|
|
return log($n)/log(10);
|
|
}
|
|
|
|
See also L</exp> for the inverse operation.
|
|
|
|
=item lstat FILEHANDLE
|
|
|
|
=item lstat EXPR
|
|
|
|
=item lstat
|
|
|
|
Does the same thing as the C<stat()> function (including setting the
|
|
special C<_> filehandle) but stats a symbolic link instead of the file
|
|
the symbolic link points to. If symbolic links are unimplemented on
|
|
your system, a normal C<stat()> is done.
|
|
|
|
If EXPR is omitted, stats C<$_>.
|
|
|
|
=item m//
|
|
|
|
The match operator. See L<perlop>.
|
|
|
|
=item map BLOCK LIST
|
|
|
|
=item map EXPR,LIST
|
|
|
|
Evaluates the BLOCK or EXPR for each element of LIST (locally setting C<$_> to each
|
|
element) and returns the list value composed of the results of each such
|
|
evaluation. Evaluates BLOCK or EXPR in a list context, so each element of LIST
|
|
may produce zero, one, or more elements in the returned value.
|
|
|
|
In scalar context, returns the total number of elements so generated.
|
|
|
|
@chars = map(chr, @nums);
|
|
|
|
translates a list of numbers to the corresponding characters. And
|
|
|
|
%hash = map { getkey($_) => $_ } @array;
|
|
|
|
is just a funny way to write
|
|
|
|
%hash = ();
|
|
foreach $_ (@array) {
|
|
$hash{getkey($_)} = $_;
|
|
}
|
|
|
|
Note that, because C<$_> is a reference into the list value, it can
|
|
be used to modify the elements of the array. While this is useful and
|
|
supported, it can cause bizarre results if the LIST is not a named array.
|
|
Using a regular C<foreach> loop for this purpose would be clearer in
|
|
most cases. See also L</grep> for an array composed of those items of
|
|
the original list for which the BLOCK or EXPR evaluates to true.
|
|
|
|
=item mkdir FILENAME,MODE
|
|
|
|
Creates the directory specified by FILENAME, with permissions
|
|
specified by MODE (as modified by C<umask>). If it succeeds it
|
|
returns TRUE, otherwise it returns FALSE and sets C<$!> (errno).
|
|
|
|
In general, it is better to create directories with permissive MODEs,
|
|
and let the user modify that with their C<umask>, than it is to supply
|
|
a restrictive MODE and give the user no way to be more permissive.
|
|
The exceptions to this rule are when the file or directory should be
|
|
kept private (mail files, for instance). The perlfunc(1) entry on
|
|
C<umask> discusses the choice of MODE in more detail.
|
|
|
|
=item msgctl ID,CMD,ARG
|
|
|
|
Calls the System V IPC function msgctl(2). You'll probably have to say
|
|
|
|
use IPC::SysV;
|
|
|
|
first to get the correct constant definitions. If CMD is C<IPC_STAT>,
|
|
then ARG must be a variable which will hold the returned C<msqid_ds>
|
|
structure. Returns like C<ioctl()>: the undefined value for error, "C<0> but
|
|
true" for zero, or the actual return value otherwise. See also
|
|
C<IPC::SysV> and C<IPC::Semaphore::Msg> documentation.
|
|
|
|
=item msgget KEY,FLAGS
|
|
|
|
Calls the System V IPC function msgget(2). Returns the message queue
|
|
id, or the undefined value if there is an error. See also C<IPC::SysV>
|
|
and C<IPC::SysV::Msg> documentation.
|
|
|
|
=item msgsnd ID,MSG,FLAGS
|
|
|
|
Calls the System V IPC function msgsnd to send the message MSG to the
|
|
message queue ID. MSG must begin with the long integer message type,
|
|
which may be created with C<pack("l", $type)>. Returns TRUE if
|
|
successful, or FALSE if there is an error. See also C<IPC::SysV>
|
|
and C<IPC::SysV::Msg> documentation.
|
|
|
|
=item msgrcv ID,VAR,SIZE,TYPE,FLAGS
|
|
|
|
Calls the System V IPC function msgrcv to receive a message from
|
|
message queue ID into variable VAR with a maximum message size of
|
|
SIZE. Note that if a message is received, the message type will be
|
|
the first thing in VAR, and the maximum length of VAR is SIZE plus the
|
|
size of the message type. Returns TRUE if successful, or FALSE if
|
|
there is an error. See also C<IPC::SysV> and C<IPC::SysV::Msg> documentation.
|
|
|
|
=item my EXPR
|
|
|
|
A C<my()> declares the listed variables to be local (lexically) to the
|
|
enclosing block, file, or C<eval()>. If
|
|
more than one value is listed, the list must be placed in parentheses. See
|
|
L<perlsub/"Private Variables via my()"> for details.
|
|
|
|
=item next LABEL
|
|
|
|
=item next
|
|
|
|
The C<next> command is like the C<continue> statement in C; it starts
|
|
the next iteration of the loop:
|
|
|
|
LINE: while (<STDIN>) {
|
|
next LINE if /^#/; # discard comments
|
|
#...
|
|
}
|
|
|
|
Note that if there were a C<continue> block on the above, it would get
|
|
executed even on discarded lines. If the LABEL is omitted, the command
|
|
refers to the innermost enclosing loop.
|
|
|
|
C<next> cannot be used to exit a block which returns a value such as
|
|
C<eval {}>, C<sub {}> or C<do {}>, and should not be used to exit
|
|
a grep() or map() operation.
|
|
|
|
See also L</continue> for an illustration of how C<last>, C<next>, and
|
|
C<redo> work.
|
|
|
|
=item no Module LIST
|
|
|
|
See the L</use> function, which C<no> is the opposite of.
|
|
|
|
=item oct EXPR
|
|
|
|
=item oct
|
|
|
|
Interprets EXPR as an octal string and returns the corresponding
|
|
value. (If EXPR happens to start off with C<0x>, interprets it as a
|
|
hex string. If EXPR starts off with C<0b>, it is interpreted as a
|
|
binary string.) The following will handle decimal, binary, octal, and
|
|
hex in the standard Perl or C notation:
|
|
|
|
$val = oct($val) if $val =~ /^0/;
|
|
|
|
If EXPR is omitted, uses C<$_>. This function is commonly used when
|
|
a string such as C<644> needs to be converted into a file mode, for
|
|
example. (Although perl will automatically convert strings into
|
|
numbers as needed, this automatic conversion assumes base 10.)
|
|
|
|
=item open FILEHANDLE,EXPR
|
|
|
|
=item open FILEHANDLE
|
|
|
|
Opens the file whose filename is given by EXPR, and associates it with
|
|
FILEHANDLE. If FILEHANDLE is an expression, its value is used as the
|
|
name of the real filehandle wanted. If EXPR is omitted, the scalar
|
|
variable of the same name as the FILEHANDLE contains the filename.
|
|
(Note that lexical variables--those declared with C<my()>--will not work
|
|
for this purpose; so if you're using C<my()>, specify EXPR in your call
|
|
to open.) See L<perlopentut> for a kinder, gentler explanation of opening
|
|
files.
|
|
|
|
If the filename begins with C<'E<lt>'> or nothing, the file is opened for input.
|
|
If the filename begins with C<'E<gt>'>, the file is truncated and opened for
|
|
output, being created if necessary. If the filename begins with C<'E<gt>E<gt>'>,
|
|
the file is opened for appending, again being created if necessary.
|
|
You can put a C<'+'> in front of the C<'E<gt>'> or C<'E<lt>'> to indicate that
|
|
you want both read and write access to the file; thus C<'+E<lt>'> is almost
|
|
always preferred for read/write updates--the C<'+E<gt>'> mode would clobber the
|
|
file first. You can't usually use either read-write mode for updating
|
|
textfiles, since they have variable length records. See the B<-i>
|
|
switch in L<perlrun> for a better approach. The file is created with
|
|
permissions of C<0666> modified by the process' C<umask> value.
|
|
|
|
The prefix and the filename may be separated with spaces.
|
|
These various prefixes correspond to the fopen(3) modes of C<'r'>, C<'r+'>, C<'w'>,
|
|
C<'w+'>, C<'a'>, and C<'a+'>.
|
|
|
|
If the filename begins with C<'|'>, the filename is interpreted as a
|
|
command to which output is to be piped, and if the filename ends with a
|
|
C<'|'>, the filename is interpreted as a command which pipes output to
|
|
us. See L<perlipc/"Using open() for IPC">
|
|
for more examples of this. (You are not allowed to C<open()> to a command
|
|
that pipes both in I<and> out, but see L<IPC::Open2>, L<IPC::Open3>,
|
|
and L<perlipc/"Bidirectional Communication"> for alternatives.)
|
|
|
|
Opening C<'-'> opens STDIN and opening C<'E<gt>-'> opens STDOUT. Open returns
|
|
nonzero upon success, the undefined value otherwise. If the C<open()>
|
|
involved a pipe, the return value happens to be the pid of the
|
|
subprocess.
|
|
|
|
If you're unfortunate enough to be running Perl on a system that
|
|
distinguishes between text files and binary files (modern operating
|
|
systems don't care), then you should check out L</binmode> for tips for
|
|
dealing with this. The key distinction between systems that need C<binmode()>
|
|
and those that don't is their text file formats. Systems like Unix, MacOS, and
|
|
Plan9, which delimit lines with a single character, and which encode that
|
|
character in C as C<"\n">, do not need C<binmode()>. The rest need it.
|
|
|
|
When opening a file, it's usually a bad idea to continue normal execution
|
|
if the request failed, so C<open()> is frequently used in connection with
|
|
C<die()>. Even if C<die()> won't do what you want (say, in a CGI script,
|
|
where you want to make a nicely formatted error message (but there are
|
|
modules that can help with that problem)) you should always check
|
|
the return value from opening a file. The infrequent exception is when
|
|
working with an unopened filehandle is actually what you want to do.
|
|
|
|
Examples:
|
|
|
|
$ARTICLE = 100;
|
|
open ARTICLE or die "Can't find article $ARTICLE: $!\n";
|
|
while (<ARTICLE>) {...
|
|
|
|
open(LOG, '>>/usr/spool/news/twitlog'); # (log is reserved)
|
|
# if the open fails, output is discarded
|
|
|
|
open(DBASE, '+<dbase.mine') # open for update
|
|
or die "Can't open 'dbase.mine' for update: $!";
|
|
|
|
open(ARTICLE, "caesar <$article |") # decrypt article
|
|
or die "Can't start caesar: $!";
|
|
|
|
open(EXTRACT, "|sort >/tmp/Tmp$$") # $$ is our process id
|
|
or die "Can't start sort: $!";
|
|
|
|
# process argument list of files along with any includes
|
|
|
|
foreach $file (@ARGV) {
|
|
process($file, 'fh00');
|
|
}
|
|
|
|
sub process {
|
|
my($filename, $input) = @_;
|
|
$input++; # this is a string increment
|
|
unless (open($input, $filename)) {
|
|
print STDERR "Can't open $filename: $!\n";
|
|
return;
|
|
}
|
|
|
|
local $_;
|
|
while (<$input>) { # note use of indirection
|
|
if (/^#include "(.*)"/) {
|
|
process($1, $input);
|
|
next;
|
|
}
|
|
#... # whatever
|
|
}
|
|
}
|
|
|
|
You may also, in the Bourne shell tradition, specify an EXPR beginning
|
|
with C<'E<gt>&'>, in which case the rest of the string is interpreted as the
|
|
name of a filehandle (or file descriptor, if numeric) to be
|
|
duped and opened. You may use C<&> after C<E<gt>>, C<E<gt>E<gt>>, C<E<lt>>, C<+E<gt>>,
|
|
C<+E<gt>E<gt>>, and C<+E<lt>>. The
|
|
mode you specify should match the mode of the original filehandle.
|
|
(Duping a filehandle does not take into account any existing contents of
|
|
stdio buffers.)
|
|
Here is a script that saves, redirects, and restores STDOUT and
|
|
STDERR:
|
|
|
|
#!/usr/bin/perl
|
|
open(OLDOUT, ">&STDOUT");
|
|
open(OLDERR, ">&STDERR");
|
|
|
|
open(STDOUT, ">foo.out") || die "Can't redirect stdout";
|
|
open(STDERR, ">&STDOUT") || die "Can't dup stdout";
|
|
|
|
select(STDERR); $| = 1; # make unbuffered
|
|
select(STDOUT); $| = 1; # make unbuffered
|
|
|
|
print STDOUT "stdout 1\n"; # this works for
|
|
print STDERR "stderr 1\n"; # subprocesses too
|
|
|
|
close(STDOUT);
|
|
close(STDERR);
|
|
|
|
open(STDOUT, ">&OLDOUT");
|
|
open(STDERR, ">&OLDERR");
|
|
|
|
print STDOUT "stdout 2\n";
|
|
print STDERR "stderr 2\n";
|
|
|
|
If you specify C<'E<lt>&=N'>, where C<N> is a number, then Perl will do an
|
|
equivalent of C's C<fdopen()> of that file descriptor; this is more
|
|
parsimonious of file descriptors. For example:
|
|
|
|
open(FILEHANDLE, "<&=$fd")
|
|
|
|
If you open a pipe on the command C<'-'>, i.e., either C<'|-'> or C<'-|'>, then
|
|
there is an implicit fork done, and the return value of open is the pid
|
|
of the child within the parent process, and C<0> within the child
|
|
process. (Use C<defined($pid)> to determine whether the open was successful.)
|
|
The filehandle behaves normally for the parent, but i/o to that
|
|
filehandle is piped from/to the STDOUT/STDIN of the child process.
|
|
In the child process the filehandle isn't opened--i/o happens from/to
|
|
the new STDOUT or STDIN. Typically this is used like the normal
|
|
piped open when you want to exercise more control over just how the
|
|
pipe command gets executed, such as when you are running setuid, and
|
|
don't want to have to scan shell commands for metacharacters.
|
|
The following pairs are more or less equivalent:
|
|
|
|
open(FOO, "|tr '[a-z]' '[A-Z]'");
|
|
open(FOO, "|-") || exec 'tr', '[a-z]', '[A-Z]';
|
|
|
|
open(FOO, "cat -n '$file'|");
|
|
open(FOO, "-|") || exec 'cat', '-n', $file;
|
|
|
|
See L<perlipc/"Safe Pipe Opens"> for more examples of this.
|
|
|
|
NOTE: On any operation that may do a fork, any unflushed buffers remain
|
|
unflushed in both processes, which means you may need to set C<$|> to
|
|
avoid duplicate output. On systems that support a close-on-exec flag on
|
|
files, the flag will be set for the newly opened file descriptor as
|
|
determined by the value of $^F. See L<perlvar/$^F>.
|
|
|
|
Closing any piped filehandle causes the parent process to wait for the
|
|
child to finish, and returns the status value in C<$?>.
|
|
|
|
The filename passed to open will have leading and trailing
|
|
whitespace deleted, and the normal redirection characters
|
|
honored. This property, known as "magic open",
|
|
can often be used to good effect. A user could specify a filename of
|
|
F<"rsh cat file |">, or you could change certain filenames as needed:
|
|
|
|
$filename =~ s/(.*\.gz)\s*$/gzip -dc < $1|/;
|
|
open(FH, $filename) or die "Can't open $filename: $!";
|
|
|
|
However, to open a file with arbitrary weird characters in it, it's
|
|
necessary to protect any leading and trailing whitespace:
|
|
|
|
$file =~ s#^(\s)#./$1#;
|
|
open(FOO, "< $file\0");
|
|
|
|
If you want a "real" C C<open()> (see L<open(2)> on your system), then you
|
|
should use the C<sysopen()> function, which involves no such magic. This is
|
|
another way to protect your filenames from interpretation. For example:
|
|
|
|
use IO::Handle;
|
|
sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL)
|
|
or die "sysopen $path: $!";
|
|
$oldfh = select(HANDLE); $| = 1; select($oldfh);
|
|
print HANDLE "stuff $$\n");
|
|
seek(HANDLE, 0, 0);
|
|
print "File contains: ", <HANDLE>;
|
|
|
|
Using the constructor from the C<IO::Handle> package (or one of its
|
|
subclasses, such as C<IO::File> or C<IO::Socket>), you can generate anonymous
|
|
filehandles that have the scope of whatever variables hold references to
|
|
them, and automatically close whenever and however you leave that scope:
|
|
|
|
use IO::File;
|
|
#...
|
|
sub read_myfile_munged {
|
|
my $ALL = shift;
|
|
my $handle = new IO::File;
|
|
open($handle, "myfile") or die "myfile: $!";
|
|
$first = <$handle>
|
|
or return (); # Automatically closed here.
|
|
mung $first or die "mung failed"; # Or here.
|
|
return $first, <$handle> if $ALL; # Or here.
|
|
$first; # Or here.
|
|
}
|
|
|
|
See L</seek> for some details about mixing reading and writing.
|
|
|
|
=item opendir DIRHANDLE,EXPR
|
|
|
|
Opens a directory named EXPR for processing by C<readdir()>, C<telldir()>,
|
|
C<seekdir()>, C<rewinddir()>, and C<closedir()>. Returns TRUE if successful.
|
|
DIRHANDLEs have their own namespace separate from FILEHANDLEs.
|
|
|
|
=item ord EXPR
|
|
|
|
=item ord
|
|
|
|
Returns the numeric ascii value of the first character of EXPR. If
|
|
EXPR is omitted, uses C<$_>. For the reverse, see L</chr>.
|
|
|
|
=item pack TEMPLATE,LIST
|
|
|
|
Takes an array or list of values and packs it into a binary structure,
|
|
returning the string containing the structure. The TEMPLATE is a
|
|
sequence of characters that give the order and type of values, as
|
|
follows:
|
|
|
|
a A string with arbitrary binary data, will be null padded.
|
|
A An ascii string, will be space padded.
|
|
Z A null terminated (asciz) string, will be null padded.
|
|
|
|
b A bit string (ascending bit order, like vec()).
|
|
B A bit string (descending bit order).
|
|
h A hex string (low nybble first).
|
|
H A hex string (high nybble first).
|
|
|
|
c A signed char value.
|
|
C An unsigned char value.
|
|
|
|
s A signed short value.
|
|
S An unsigned short value.
|
|
(This 'short' is _exactly_ 16 bits, which may differ from
|
|
what a local C compiler calls 'short'.)
|
|
|
|
i A signed integer value.
|
|
I An unsigned integer value.
|
|
(This 'integer' is _at least_ 32 bits wide. Its exact
|
|
size depends on what a local C compiler calls 'int',
|
|
and may even be larger than the 'long' described in
|
|
the next item.)
|
|
|
|
l A signed long value.
|
|
L An unsigned long value.
|
|
(This 'long' is _exactly_ 32 bits, which may differ from
|
|
what a local C compiler calls 'long'.)
|
|
|
|
n A short in "network" (big-endian) order.
|
|
N A long in "network" (big-endian) order.
|
|
v A short in "VAX" (little-endian) order.
|
|
V A long in "VAX" (little-endian) order.
|
|
(These 'shorts' and 'longs' are _exactly_ 16 bits and
|
|
_exactly_ 32 bits, respectively.)
|
|
|
|
q A signed quad (64-bit) value.
|
|
Q An unsigned quad value.
|
|
(Available only if your system supports 64-bit integer values
|
|
_and_ if Perl has been compiled to support those.
|
|
Causes a fatal error otherwise.)
|
|
|
|
f A single-precision float in the native format.
|
|
d A double-precision float in the native format.
|
|
|
|
p A pointer to a null-terminated string.
|
|
P A pointer to a structure (fixed-length string).
|
|
|
|
u A uuencoded string.
|
|
|
|
w A BER compressed integer. Its bytes represent an unsigned
|
|
integer in base 128, most significant digit first, with as
|
|
few digits as possible. Bit eight (the high bit) is set
|
|
on each byte except the last.
|
|
|
|
x A null byte.
|
|
X Back up a byte.
|
|
@ Null fill to absolute position.
|
|
|
|
The following rules apply:
|
|
|
|
=over 8
|
|
|
|
=item *
|
|
|
|
Each letter may optionally be followed by a number giving a repeat
|
|
count. With all types except C<"a">, C<"A">, C<"Z">, C<"b">, C<"B">, C<"h">,
|
|
C<"H">, and C<"P"> the pack function will gobble up that many values from
|
|
the LIST. A C<*> for the repeat count means to use however many items are
|
|
left.
|
|
|
|
=item *
|
|
|
|
The C<"a">, C<"A">, and C<"Z"> types gobble just one value, but pack it as a
|
|
string of length count, padding with nulls or spaces as necessary. When
|
|
unpacking, C<"A"> strips trailing spaces and nulls, C<"Z"> strips everything
|
|
after the first null, and C<"a"> returns data verbatim.
|
|
|
|
=item *
|
|
|
|
Likewise, the C<"b"> and C<"B"> fields pack a string that many bits long.
|
|
|
|
=item *
|
|
|
|
The C<"h"> and C<"H"> fields pack a string that many nybbles long.
|
|
|
|
=item *
|
|
|
|
The C<"p"> type packs a pointer to a null-terminated string. You are
|
|
responsible for ensuring the string is not a temporary value (which can
|
|
potentially get deallocated before you get around to using the packed result).
|
|
The C<"P"> type packs a pointer to a structure of the size indicated by the
|
|
length. A NULL pointer is created if the corresponding value for C<"p"> or
|
|
C<"P"> is C<undef>.
|
|
|
|
=item *
|
|
|
|
The integer formats C<"s">, C<"S">, C<"i">, C<"I">, C<"l">, and C<"L">
|
|
are inherently non-portable between processors and operating systems
|
|
because they obey the native byteorder and endianness. For example a
|
|
4-byte integer 0x87654321 (2271560481 decimal) be ordered natively
|
|
(arranged in and handled by the CPU registers) into bytes as
|
|
|
|
0x12 0x34 0x56 0x78 # little-endian
|
|
0x78 0x56 0x34 0x12 # big-endian
|
|
|
|
Basically, the Intel, Alpha, and VAX CPUs and little-endian, while
|
|
everybody else, for example Motorola m68k/88k, PPC, Sparc, HP PA,
|
|
Power, and Cray are big-endian. MIPS can be either: Digital used it
|
|
in little-endian mode, SGI uses it in big-endian mode.
|
|
|
|
The names `big-endian' and `little-endian' are joking references to
|
|
the classic "Gulliver's Travels" (via the paper "On Holy Wars and a
|
|
Plea for Peace" by Danny Cohen, USC/ISI IEN 137, April 1, 1980) and
|
|
the egg-eating habits of the lilliputs.
|
|
|
|
Some systems may even have weird byte orders such as
|
|
|
|
0x56 0x78 0x12 0x34
|
|
0x34 0x12 0x78 0x56
|
|
|
|
You can see your system's preference with
|
|
|
|
print join(" ", map { sprintf "%#02x", $_ }
|
|
unpack("C*",pack("L",0x12345678))), "\n";
|
|
|
|
The byteorder on the platform where Perl was built is also available
|
|
via L<Config>:
|
|
|
|
use Config;
|
|
print $Config{byteorder}, "\n";
|
|
|
|
Byteorders C<'1234'> and C<'12345678'> are little-endian, C<'4321'>
|
|
and C<'87654321'> are big-endian.
|
|
|
|
If you want portable packed integers use the formats C<"n">, C<"N">,
|
|
C<"v">, and C<"V">, their byte endianness and size is known.
|
|
|
|
=item *
|
|
|
|
Real numbers (floats and doubles) are in the native machine format only;
|
|
due to the multiplicity of floating formats around, and the lack of a
|
|
standard "network" representation, no facility for interchange has been
|
|
made. This means that packed floating point data written on one machine
|
|
may not be readable on another - even if both use IEEE floating point
|
|
arithmetic (as the endian-ness of the memory representation is not part
|
|
of the IEEE spec).
|
|
|
|
Note that Perl uses doubles internally for all numeric calculation, and
|
|
converting from double into float and thence back to double again will
|
|
lose precision (i.e., C<unpack("f", pack("f", $foo)>) will not in general
|
|
equal C<$foo>).
|
|
|
|
=back
|
|
|
|
Examples:
|
|
|
|
$foo = pack("CCCC",65,66,67,68);
|
|
# foo eq "ABCD"
|
|
$foo = pack("C4",65,66,67,68);
|
|
# same thing
|
|
|
|
$foo = pack("ccxxcc",65,66,67,68);
|
|
# foo eq "AB\0\0CD"
|
|
|
|
$foo = pack("s2",1,2);
|
|
# "\1\0\2\0" on little-endian
|
|
# "\0\1\0\2" on big-endian
|
|
|
|
$foo = pack("a4","abcd","x","y","z");
|
|
# "abcd"
|
|
|
|
$foo = pack("aaaa","abcd","x","y","z");
|
|
# "axyz"
|
|
|
|
$foo = pack("a14","abcdefg");
|
|
# "abcdefg\0\0\0\0\0\0\0"
|
|
|
|
$foo = pack("i9pl", gmtime);
|
|
# a real struct tm (on my system anyway)
|
|
|
|
$utmp_template = "Z8 Z8 Z16 L";
|
|
$utmp = pack($utmp_template, @utmp1);
|
|
# a struct utmp (BSDish)
|
|
|
|
@utmp2 = unpack($utmp_template, $utmp);
|
|
# "@utmp1" eq "@utmp2"
|
|
|
|
sub bintodec {
|
|
unpack("N", pack("B32", substr("0" x 32 . shift, -32)));
|
|
}
|
|
|
|
The same template may generally also be used in unpack().
|
|
|
|
=item package
|
|
|
|
=item package NAMESPACE
|
|
|
|
Declares the compilation unit as being in the given namespace. The scope
|
|
of the package declaration is from the declaration itself through the end
|
|
of the enclosing block, file, or eval (the same as the C<my()> operator).
|
|
All further unqualified dynamic identifiers will be in this namespace.
|
|
A package statement affects only dynamic variables--including those
|
|
you've used C<local()> on--but I<not> lexical variables, which are created
|
|
with C<my()>. Typically it would be the first declaration in a file to
|
|
be included by the C<require> or C<use> operator. You can switch into a
|
|
package in more than one place; it merely influences which symbol table
|
|
is used by the compiler for the rest of that block. You can refer to
|
|
variables and filehandles in other packages by prefixing the identifier
|
|
with the package name and a double colon: C<$Package::Variable>.
|
|
If the package name is null, the C<main> package as assumed. That is,
|
|
C<$::sail> is equivalent to C<$main::sail> (as well as to C<$main'sail>,
|
|
still seen in older code).
|
|
|
|
If NAMESPACE is omitted, then there is no current package, and all
|
|
identifiers must be fully qualified or lexicals. This is stricter
|
|
than C<use strict>, since it also extends to function names.
|
|
|
|
See L<perlmod/"Packages"> for more information about packages, modules,
|
|
and classes. See L<perlsub> for other scoping issues.
|
|
|
|
=item pipe READHANDLE,WRITEHANDLE
|
|
|
|
Opens a pair of connected pipes like the corresponding system call.
|
|
Note that if you set up a loop of piped processes, deadlock can occur
|
|
unless you are very careful. In addition, note that Perl's pipes use
|
|
stdio buffering, so you may need to set C<$|> to flush your WRITEHANDLE
|
|
after each command, depending on the application.
|
|
|
|
See L<IPC::Open2>, L<IPC::Open3>, and L<perlipc/"Bidirectional Communication">
|
|
for examples of such things.
|
|
|
|
On systems that support a close-on-exec flag on files, the flag will be set
|
|
for the newly opened file descriptors as determined by the value of $^F.
|
|
See L<perlvar/$^F>.
|
|
|
|
=item pop ARRAY
|
|
|
|
=item pop
|
|
|
|
Pops and returns the last value of the array, shortening the array by
|
|
one element. Has a similar effect to
|
|
|
|
$tmp = $ARRAY[$#ARRAY--];
|
|
|
|
If there are no elements in the array, returns the undefined value.
|
|
If ARRAY is omitted, pops the C<@ARGV> array in the main program, and
|
|
the C<@_> array in subroutines, just like C<shift()>.
|
|
|
|
=item pos SCALAR
|
|
|
|
=item pos
|
|
|
|
Returns the offset of where the last C<m//g> search left off for the variable
|
|
is in question (C<$_> is used when the variable is not specified). May be
|
|
modified to change that offset. Such modification will also influence
|
|
the C<\G> zero-width assertion in regular expressions. See L<perlre> and
|
|
L<perlop>.
|
|
|
|
=item print FILEHANDLE LIST
|
|
|
|
=item print LIST
|
|
|
|
=item print
|
|
|
|
Prints a string or a comma-separated list of strings. Returns TRUE
|
|
if successful. FILEHANDLE may be a scalar variable name, in which case
|
|
the variable contains the name of or a reference to the filehandle, thus
|
|
introducing one level of indirection. (NOTE: If FILEHANDLE is a variable
|
|
and the next token is a term, it may be misinterpreted as an operator
|
|
unless you interpose a C<+> or put parentheses around the arguments.)
|
|
If FILEHANDLE is omitted, prints by default to standard output (or to the
|
|
last selected output channel--see L</select>). If LIST is also omitted,
|
|
prints C<$_> to the currently selected output channel. To set the default
|
|
output channel to something other than STDOUT use the select operation.
|
|
Note that, because print takes a LIST, anything in the LIST is evaluated
|
|
in list context, and any subroutine that you call will have one or
|
|
more of its expressions evaluated in list context. Also be careful
|
|
not to follow the print keyword with a left parenthesis unless you want
|
|
the corresponding right parenthesis to terminate the arguments to the
|
|
print--interpose a C<+> or put parentheses around all the arguments.
|
|
|
|
Note that if you're storing FILEHANDLES in an array or other expression,
|
|
you will have to use a block returning its value instead:
|
|
|
|
print { $files[$i] } "stuff\n";
|
|
print { $OK ? STDOUT : STDERR } "stuff\n";
|
|
|
|
=item printf FILEHANDLE FORMAT, LIST
|
|
|
|
=item printf FORMAT, LIST
|
|
|
|
Equivalent to C<print FILEHANDLE sprintf(FORMAT, LIST)>, except that C<$\>
|
|
(the output record separator) is not appended. The first argument
|
|
of the list will be interpreted as the C<printf()> format. If C<use locale> is
|
|
in effect, the character used for the decimal point in formatted real numbers
|
|
is affected by the LC_NUMERIC locale. See L<perllocale>.
|
|
|
|
Don't fall into the trap of using a C<printf()> when a simple
|
|
C<print()> would do. The C<print()> is more efficient and less
|
|
error prone.
|
|
|
|
=item prototype FUNCTION
|
|
|
|
Returns the prototype of a function as a string (or C<undef> if the
|
|
function has no prototype). FUNCTION is a reference to, or the name of,
|
|
the function whose prototype you want to retrieve.
|
|
|
|
If FUNCTION is a string starting with C<CORE::>, the rest is taken as a
|
|
name for Perl builtin. If the builtin is not I<overridable> (such as
|
|
C<qw//>) or its arguments cannot be expressed by a prototype (such as
|
|
C<system()>) returns C<undef> because the builtin does not really behave
|
|
like a Perl function. Otherwise, the string describing the equivalent
|
|
prototype is returned.
|
|
|
|
=item push ARRAY,LIST
|
|
|
|
Treats ARRAY as a stack, and pushes the values of LIST
|
|
onto the end of ARRAY. The length of ARRAY increases by the length of
|
|
LIST. Has the same effect as
|
|
|
|
for $value (LIST) {
|
|
$ARRAY[++$#ARRAY] = $value;
|
|
}
|
|
|
|
but is more efficient. Returns the new number of elements in the array.
|
|
|
|
=item q/STRING/
|
|
|
|
=item qq/STRING/
|
|
|
|
=item qr/STRING/
|
|
|
|
=item qx/STRING/
|
|
|
|
=item qw/STRING/
|
|
|
|
Generalized quotes. See L<perlop/"Regexp Quote-Like Operators">.
|
|
|
|
=item quotemeta EXPR
|
|
|
|
=item quotemeta
|
|
|
|
Returns the value of EXPR with all non-alphanumeric
|
|
characters backslashed. (That is, all characters not matching
|
|
C</[A-Za-z_0-9]/> will be preceded by a backslash in the
|
|
returned string, regardless of any locale settings.)
|
|
This is the internal function implementing
|
|
the C<\Q> escape in double-quoted strings.
|
|
|
|
If EXPR is omitted, uses C<$_>.
|
|
|
|
=item rand EXPR
|
|
|
|
=item rand
|
|
|
|
Returns a random fractional number greater than or equal to C<0> and less
|
|
than the value of EXPR. (EXPR should be positive.) If EXPR is
|
|
omitted, the value C<1> is used. Automatically calls C<srand()> unless
|
|
C<srand()> has already been called. See also C<srand()>.
|
|
|
|
(Note: If your rand function consistently returns numbers that are too
|
|
large or too small, then your version of Perl was probably compiled
|
|
with the wrong number of RANDBITS.)
|
|
|
|
=item read FILEHANDLE,SCALAR,LENGTH,OFFSET
|
|
|
|
=item read FILEHANDLE,SCALAR,LENGTH
|
|
|
|
Attempts to read LENGTH bytes of data into variable SCALAR from the
|
|
specified FILEHANDLE. Returns the number of bytes actually read,
|
|
C<0> at end of file, or undef if there was an error. SCALAR will be grown
|
|
or shrunk to the length actually read. An OFFSET may be specified to
|
|
place the read data at some other place than the beginning of the
|
|
string. This call is actually implemented in terms of stdio's fread(3)
|
|
call. To get a true read(2) system call, see C<sysread()>.
|
|
|
|
=item readdir DIRHANDLE
|
|
|
|
Returns the next directory entry for a directory opened by C<opendir()>.
|
|
If used in list context, returns all the rest of the entries in the
|
|
directory. If there are no more entries, returns an undefined value in
|
|
scalar context or a null list in list context.
|
|
|
|
If you're planning to filetest the return values out of a C<readdir()>, you'd
|
|
better prepend the directory in question. Otherwise, because we didn't
|
|
C<chdir()> there, it would have been testing the wrong file.
|
|
|
|
opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!";
|
|
@dots = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR);
|
|
closedir DIR;
|
|
|
|
=item readline EXPR
|
|
|
|
Reads from the filehandle whose typeglob is contained in EXPR. In scalar
|
|
context, each call reads and returns the next line, until end-of-file is
|
|
reached, whereupon the subsequent call returns undef. In list context,
|
|
reads until end-of-file is reached and returns a list of lines. Note that
|
|
the notion of "line" used here is however you may have defined it
|
|
with C<$/> or C<$INPUT_RECORD_SEPARATOR>). See L<perlvar/"$/">.
|
|
|
|
When C<$/> is set to C<undef>, when readline() is in scalar
|
|
context (i.e. file slurp mode), and when an empty file is read, it
|
|
returns C<''> the first time, followed by C<undef> subsequently.
|
|
|
|
This is the internal function implementing the C<E<lt>EXPRE<gt>>
|
|
operator, but you can use it directly. The C<E<lt>EXPRE<gt>>
|
|
operator is discussed in more detail in L<perlop/"I/O Operators">.
|
|
|
|
$line = <STDIN>;
|
|
$line = readline(*STDIN); # same thing
|
|
|
|
=item readlink EXPR
|
|
|
|
=item readlink
|
|
|
|
Returns the value of a symbolic link, if symbolic links are
|
|
implemented. If not, gives a fatal error. If there is some system
|
|
error, returns the undefined value and sets C<$!> (errno). If EXPR is
|
|
omitted, uses C<$_>.
|
|
|
|
=item readpipe EXPR
|
|
|
|
EXPR is executed as a system command.
|
|
The collected standard output of the command is returned.
|
|
In scalar context, it comes back as a single (potentially
|
|
multi-line) string. In list context, returns a list of lines
|
|
(however you've defined lines with C<$/> or C<$INPUT_RECORD_SEPARATOR>).
|
|
This is the internal function implementing the C<qx/EXPR/>
|
|
operator, but you can use it directly. The C<qx/EXPR/>
|
|
operator is discussed in more detail in L<perlop/"I/O Operators">.
|
|
|
|
=item recv SOCKET,SCALAR,LENGTH,FLAGS
|
|
|
|
Receives a message on a socket. Attempts to receive LENGTH bytes of
|
|
data into variable SCALAR from the specified SOCKET filehandle.
|
|
Actually does a C C<recvfrom()>, so that it can return the address of the
|
|
sender. Returns the undefined value if there's an error. SCALAR will
|
|
be grown or shrunk to the length actually read. Takes the same flags
|
|
as the system call of the same name.
|
|
See L<perlipc/"UDP: Message Passing"> for examples.
|
|
|
|
=item redo LABEL
|
|
|
|
=item redo
|
|
|
|
The C<redo> command restarts the loop block without evaluating the
|
|
conditional again. The C<continue> block, if any, is not executed. If
|
|
the LABEL is omitted, the command refers to the innermost enclosing
|
|
loop. This command is normally used by programs that want to lie to
|
|
themselves about what was just input:
|
|
|
|
# a simpleminded Pascal comment stripper
|
|
# (warning: assumes no { or } in strings)
|
|
LINE: while (<STDIN>) {
|
|
while (s|({.*}.*){.*}|$1 |) {}
|
|
s|{.*}| |;
|
|
if (s|{.*| |) {
|
|
$front = $_;
|
|
while (<STDIN>) {
|
|
if (/}/) { # end of comment?
|
|
s|^|$front\{|;
|
|
redo LINE;
|
|
}
|
|
}
|
|
}
|
|
print;
|
|
}
|
|
|
|
C<redo> cannot be used to retry a block which returns a value such as
|
|
C<eval {}>, C<sub {}> or C<do {}>, and should not be used to exit
|
|
a grep() or map() operation.
|
|
|
|
See also L</continue> for an illustration of how C<last>, C<next>, and
|
|
C<redo> work.
|
|
|
|
=item ref EXPR
|
|
|
|
=item ref
|
|
|
|
Returns a TRUE value if EXPR is a reference, FALSE otherwise. If EXPR
|
|
is not specified, C<$_> will be used. The value returned depends on the
|
|
type of thing the reference is a reference to.
|
|
Builtin types include:
|
|
|
|
REF
|
|
SCALAR
|
|
ARRAY
|
|
HASH
|
|
CODE
|
|
GLOB
|
|
|
|
If the referenced object has been blessed into a package, then that package
|
|
name is returned instead. You can think of C<ref()> as a C<typeof()> operator.
|
|
|
|
if (ref($r) eq "HASH") {
|
|
print "r is a reference to a hash.\n";
|
|
}
|
|
unless (ref($r)) {
|
|
print "r is not a reference at all.\n";
|
|
}
|
|
if (UNIVERSAL::isa($r, "HASH")) { # for subclassing
|
|
print "r is a reference to something that isa hash.\n";
|
|
}
|
|
|
|
See also L<perlref>.
|
|
|
|
=item rename OLDNAME,NEWNAME
|
|
|
|
Changes the name of a file. Returns C<1> for success, C<0> otherwise.
|
|
Behavior of this function varies wildly depending on your system
|
|
implementation. For example, it will usually not work across file system
|
|
boundaries, even though the system I<mv> command sometimes compensates
|
|
for this. Other restrictions include whether it works on directories,
|
|
open files, or pre-existing files. Check L<perlport> and either the
|
|
rename(2) manpage or equivalent system documentation for details.
|
|
|
|
=item require EXPR
|
|
|
|
=item require
|
|
|
|
Demands some semantics specified by EXPR, or by C<$_> if EXPR is not
|
|
supplied. If EXPR is numeric, demands that the current version of Perl
|
|
(C<$]> or $PERL_VERSION) be equal or greater than EXPR.
|
|
|
|
Otherwise, demands that a library file be included if it hasn't already
|
|
been included. The file is included via the do-FILE mechanism, which is
|
|
essentially just a variety of C<eval()>. Has semantics similar to the following
|
|
subroutine:
|
|
|
|
sub require {
|
|
my($filename) = @_;
|
|
return 1 if $INC{$filename};
|
|
my($realfilename,$result);
|
|
ITER: {
|
|
foreach $prefix (@INC) {
|
|
$realfilename = "$prefix/$filename";
|
|
if (-f $realfilename) {
|
|
$result = do $realfilename;
|
|
last ITER;
|
|
}
|
|
}
|
|
die "Can't find $filename in \@INC";
|
|
}
|
|
die $@ if $@;
|
|
die "$filename did not return true value" unless $result;
|
|
$INC{$filename} = $realfilename;
|
|
return $result;
|
|
}
|
|
|
|
Note that the file will not be included twice under the same specified
|
|
name. The file must return TRUE as the last statement to indicate
|
|
successful execution of any initialization code, so it's customary to
|
|
end such a file with "C<1;>" unless you're sure it'll return TRUE
|
|
otherwise. But it's better just to put the "C<1;>", in case you add more
|
|
statements.
|
|
|
|
If EXPR is a bareword, the require assumes a "F<.pm>" extension and
|
|
replaces "F<::>" with "F</>" in the filename for you,
|
|
to make it easy to load standard modules. This form of loading of
|
|
modules does not risk altering your namespace.
|
|
|
|
In other words, if you try this:
|
|
|
|
require Foo::Bar; # a splendid bareword
|
|
|
|
The require function will actually look for the "F<Foo/Bar.pm>" file in the
|
|
directories specified in the C<@INC> array.
|
|
|
|
But if you try this:
|
|
|
|
$class = 'Foo::Bar';
|
|
require $class; # $class is not a bareword
|
|
#or
|
|
require "Foo::Bar"; # not a bareword because of the ""
|
|
|
|
The require function will look for the "F<Foo::Bar>" file in the @INC array and
|
|
will complain about not finding "F<Foo::Bar>" there. In this case you can do:
|
|
|
|
eval "require $class";
|
|
|
|
For a yet-more-powerful import facility, see L</use> and L<perlmod>.
|
|
|
|
=item reset EXPR
|
|
|
|
=item reset
|
|
|
|
Generally used in a C<continue> block at the end of a loop to clear
|
|
variables and reset C<??> searches so that they work again. The
|
|
expression is interpreted as a list of single characters (hyphens
|
|
allowed for ranges). All variables and arrays beginning with one of
|
|
those letters are reset to their pristine state. If the expression is
|
|
omitted, one-match searches (C<?pattern?>) are reset to match again. Resets
|
|
only variables or searches in the current package. Always returns
|
|
1. Examples:
|
|
|
|
reset 'X'; # reset all X variables
|
|
reset 'a-z'; # reset lower case variables
|
|
reset; # just reset ?one-time? searches
|
|
|
|
Resetting C<"A-Z"> is not recommended because you'll wipe out your
|
|
C<@ARGV> and C<@INC> arrays and your C<%ENV> hash. Resets only package
|
|
variables--lexical variables are unaffected, but they clean themselves
|
|
up on scope exit anyway, so you'll probably want to use them instead.
|
|
See L</my>.
|
|
|
|
=item return EXPR
|
|
|
|
=item return
|
|
|
|
Returns from a subroutine, C<eval()>, or C<do FILE> with the value
|
|
given in EXPR. Evaluation of EXPR may be in list, scalar, or void
|
|
context, depending on how the return value will be used, and the context
|
|
may vary from one execution to the next (see C<wantarray()>). If no EXPR
|
|
is given, returns an empty list in list context, the undefined value in
|
|
scalar context, and (of course) nothing at all in a void context.
|
|
|
|
(Note that in the absence of a explicit C<return>, a subroutine, eval,
|
|
or do FILE will automatically return the value of the last expression
|
|
evaluated.)
|
|
|
|
=item reverse LIST
|
|
|
|
In list context, returns a list value consisting of the elements
|
|
of LIST in the opposite order. In scalar context, concatenates the
|
|
elements of LIST and returns a string value with all characters
|
|
in the opposite order.
|
|
|
|
print reverse <>; # line tac, last line first
|
|
|
|
undef $/; # for efficiency of <>
|
|
print scalar reverse <>; # character tac, last line tsrif
|
|
|
|
This operator is also handy for inverting a hash, although there are some
|
|
caveats. If a value is duplicated in the original hash, only one of those
|
|
can be represented as a key in the inverted hash. Also, this has to
|
|
unwind one hash and build a whole new one, which may take some time
|
|
on a large hash, such as from a DBM file.
|
|
|
|
%by_name = reverse %by_address; # Invert the hash
|
|
|
|
=item rewinddir DIRHANDLE
|
|
|
|
Sets the current position to the beginning of the directory for the
|
|
C<readdir()> routine on DIRHANDLE.
|
|
|
|
=item rindex STR,SUBSTR,POSITION
|
|
|
|
=item rindex STR,SUBSTR
|
|
|
|
Works just like index() except that it returns the position of the LAST
|
|
occurrence of SUBSTR in STR. If POSITION is specified, returns the
|
|
last occurrence at or before that position.
|
|
|
|
=item rmdir FILENAME
|
|
|
|
=item rmdir
|
|
|
|
Deletes the directory specified by FILENAME if that directory is empty. If it
|
|
succeeds it returns TRUE, otherwise it returns FALSE and sets C<$!> (errno). If
|
|
FILENAME is omitted, uses C<$_>.
|
|
|
|
=item s///
|
|
|
|
The substitution operator. See L<perlop>.
|
|
|
|
=item scalar EXPR
|
|
|
|
Forces EXPR to be interpreted in scalar context and returns the value
|
|
of EXPR.
|
|
|
|
@counts = ( scalar @a, scalar @b, scalar @c );
|
|
|
|
There is no equivalent operator to force an expression to
|
|
be interpolated in list context because in practice, this is never
|
|
needed. If you really wanted to do so, however, you could use
|
|
the construction C<@{[ (some expression) ]}>, but usually a simple
|
|
C<(some expression)> suffices.
|
|
|
|
Since C<scalar> is a unary operator, if you accidentally use for EXPR a
|
|
parenthesized list, this behaves as a scalar comma expression, evaluating
|
|
all but the last element in void context and returning the final element
|
|
evaluated in scalar context. This is seldom what you want.
|
|
|
|
The following single statement:
|
|
|
|
print uc(scalar(&foo,$bar)),$baz;
|
|
|
|
is the moral equivalent of these two:
|
|
|
|
&foo;
|
|
print(uc($bar),$baz);
|
|
|
|
See L<perlop> for more details on unary operators and the comma operator.
|
|
|
|
=item seek FILEHANDLE,POSITION,WHENCE
|
|
|
|
Sets FILEHANDLE's position, just like the C<fseek()> call of C<stdio()>.
|
|
FILEHANDLE may be an expression whose value gives the name of the
|
|
filehandle. The values for WHENCE are C<0> to set the new position to
|
|
POSITION, C<1> to set it to the current position plus POSITION, and C<2> to
|
|
set it to EOF plus POSITION (typically negative). For WHENCE you may
|
|
use the constants C<SEEK_SET>, C<SEEK_CUR>, and C<SEEK_END> from either the
|
|
C<IO::Seekable> or the POSIX module. Returns C<1> upon success, C<0> otherwise.
|
|
|
|
If you want to position file for C<sysread()> or C<syswrite()>, don't use
|
|
C<seek()> -- buffering makes its effect on the file's system position
|
|
unpredictable and non-portable. Use C<sysseek()> instead.
|
|
|
|
Due to the rules and rigors of ANSI C, on some systems you have to do a
|
|
seek whenever you switch between reading and writing. Amongst other
|
|
things, this may have the effect of calling stdio's clearerr(3).
|
|
A WHENCE of C<1> (C<SEEK_CUR>) is useful for not moving the file position:
|
|
|
|
seek(TEST,0,1);
|
|
|
|
This is also useful for applications emulating C<tail -f>. Once you hit
|
|
EOF on your read, and then sleep for a while, you might have to stick in a
|
|
seek() to reset things. The C<seek()> doesn't change the current position,
|
|
but it I<does> clear the end-of-file condition on the handle, so that the
|
|
next C<E<lt>FILEE<gt>> makes Perl try again to read something. We hope.
|
|
|
|
If that doesn't work (some stdios are particularly cantankerous), then
|
|
you may need something more like this:
|
|
|
|
for (;;) {
|
|
for ($curpos = tell(FILE); $_ = <FILE>;
|
|
$curpos = tell(FILE)) {
|
|
# search for some stuff and put it into files
|
|
}
|
|
sleep($for_a_while);
|
|
seek(FILE, $curpos, 0);
|
|
}
|
|
|
|
=item seekdir DIRHANDLE,POS
|
|
|
|
Sets the current position for the C<readdir()> routine on DIRHANDLE. POS
|
|
must be a value returned by C<telldir()>. Has the same caveats about
|
|
possible directory compaction as the corresponding system library
|
|
routine.
|
|
|
|
=item select FILEHANDLE
|
|
|
|
=item select
|
|
|
|
Returns the currently selected filehandle. Sets the current default
|
|
filehandle for output, if FILEHANDLE is supplied. This has two
|
|
effects: first, a C<write()> or a C<print()> without a filehandle will
|
|
default to this FILEHANDLE. Second, references to variables related to
|
|
output will refer to this output channel. For example, if you have to
|
|
set the top of form format for more than one output channel, you might
|
|
do the following:
|
|
|
|
select(REPORT1);
|
|
$^ = 'report1_top';
|
|
select(REPORT2);
|
|
$^ = 'report2_top';
|
|
|
|
FILEHANDLE may be an expression whose value gives the name of the
|
|
actual filehandle. Thus:
|
|
|
|
$oldfh = select(STDERR); $| = 1; select($oldfh);
|
|
|
|
Some programmers may prefer to think of filehandles as objects with
|
|
methods, preferring to write the last example as:
|
|
|
|
use IO::Handle;
|
|
STDERR->autoflush(1);
|
|
|
|
=item select RBITS,WBITS,EBITS,TIMEOUT
|
|
|
|
This calls the select(2) system call with the bit masks specified, which
|
|
can be constructed using C<fileno()> and C<vec()>, along these lines:
|
|
|
|
$rin = $win = $ein = '';
|
|
vec($rin,fileno(STDIN),1) = 1;
|
|
vec($win,fileno(STDOUT),1) = 1;
|
|
$ein = $rin | $win;
|
|
|
|
If you want to select on many filehandles you might wish to write a
|
|
subroutine:
|
|
|
|
sub fhbits {
|
|
my(@fhlist) = split(' ',$_[0]);
|
|
my($bits);
|
|
for (@fhlist) {
|
|
vec($bits,fileno($_),1) = 1;
|
|
}
|
|
$bits;
|
|
}
|
|
$rin = fhbits('STDIN TTY SOCK');
|
|
|
|
The usual idiom is:
|
|
|
|
($nfound,$timeleft) =
|
|
select($rout=$rin, $wout=$win, $eout=$ein, $timeout);
|
|
|
|
or to block until something becomes ready just do this
|
|
|
|
$nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef);
|
|
|
|
Most systems do not bother to return anything useful in C<$timeleft>, so
|
|
calling select() in scalar context just returns C<$nfound>.
|
|
|
|
Any of the bit masks can also be undef. The timeout, if specified, is
|
|
in seconds, which may be fractional. Note: not all implementations are
|
|
capable of returning theC<$timeleft>. If not, they always return
|
|
C<$timeleft> equal to the supplied C<$timeout>.
|
|
|
|
You can effect a sleep of 250 milliseconds this way:
|
|
|
|
select(undef, undef, undef, 0.25);
|
|
|
|
B<WARNING>: One should not attempt to mix buffered I/O (like C<read()>
|
|
or E<lt>FHE<gt>) with C<select()>, except as permitted by POSIX, and even
|
|
then only on POSIX systems. You have to use C<sysread()> instead.
|
|
|
|
=item semctl ID,SEMNUM,CMD,ARG
|
|
|
|
Calls the System V IPC function C<semctl()>. You'll probably have to say
|
|
|
|
use IPC::SysV;
|
|
|
|
first to get the correct constant definitions. If CMD is IPC_STAT or
|
|
GETALL, then ARG must be a variable which will hold the returned
|
|
semid_ds structure or semaphore value array. Returns like C<ioctl()>: the
|
|
undefined value for error, "C<0> but true" for zero, or the actual return
|
|
value otherwise. See also C<IPC::SysV> and C<IPC::Semaphore> documentation.
|
|
|
|
=item semget KEY,NSEMS,FLAGS
|
|
|
|
Calls the System V IPC function semget. Returns the semaphore id, or
|
|
the undefined value if there is an error. See also C<IPC::SysV> and
|
|
C<IPC::SysV::Semaphore> documentation.
|
|
|
|
=item semop KEY,OPSTRING
|
|
|
|
Calls the System V IPC function semop to perform semaphore operations
|
|
such as signaling and waiting. OPSTRING must be a packed array of
|
|
semop structures. Each semop structure can be generated with
|
|
C<pack("sss", $semnum, $semop, $semflag)>. The number of semaphore
|
|
operations is implied by the length of OPSTRING. Returns TRUE if
|
|
successful, or FALSE if there is an error. As an example, the
|
|
following code waits on semaphore C<$semnum> of semaphore id C<$semid>:
|
|
|
|
$semop = pack("sss", $semnum, -1, 0);
|
|
die "Semaphore trouble: $!\n" unless semop($semid, $semop);
|
|
|
|
To signal the semaphore, replace C<-1> with C<1>. See also C<IPC::SysV>
|
|
and C<IPC::SysV::Semaphore> documentation.
|
|
|
|
=item send SOCKET,MSG,FLAGS,TO
|
|
|
|
=item send SOCKET,MSG,FLAGS
|
|
|
|
Sends a message on a socket. Takes the same flags as the system call
|
|
of the same name. On unconnected sockets you must specify a
|
|
destination to send TO, in which case it does a C C<sendto()>. Returns
|
|
the number of characters sent, or the undefined value if there is an
|
|
error. The C system call sendmsg(2) is currently unimplemented.
|
|
See L<perlipc/"UDP: Message Passing"> for examples.
|
|
|
|
=item setpgrp PID,PGRP
|
|
|
|
Sets the current process group for the specified PID, C<0> for the current
|
|
process. Will produce a fatal error if used on a machine that doesn't
|
|
implement setpgrp(2). If the arguments are omitted, it defaults to
|
|
C<0,0>. Note that the POSIX version of C<setpgrp()> does not accept any
|
|
arguments, so only C<setpgrp(0,0)> is portable. See also C<POSIX::setsid()>.
|
|
|
|
=item setpriority WHICH,WHO,PRIORITY
|
|
|
|
Sets the current priority for a process, a process group, or a user.
|
|
(See setpriority(2).) Will produce a fatal error if used on a machine
|
|
that doesn't implement setpriority(2).
|
|
|
|
=item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
|
|
|
|
Sets the socket option requested. Returns undefined if there is an
|
|
error. OPTVAL may be specified as C<undef> if you don't want to pass an
|
|
argument.
|
|
|
|
=item shift ARRAY
|
|
|
|
=item shift
|
|
|
|
Shifts the first value of the array off and returns it, shortening the
|
|
array by 1 and moving everything down. If there are no elements in the
|
|
array, returns the undefined value. If ARRAY is omitted, shifts the
|
|
C<@_> array within the lexical scope of subroutines and formats, and the
|
|
C<@ARGV> array at file scopes or within the lexical scopes established by
|
|
the C<eval ''>, C<BEGIN {}>, C<END {}>, and C<INIT {}> constructs.
|
|
See also C<unshift()>, C<push()>, and C<pop()>. C<Shift()> and C<unshift()> do the
|
|
same thing to the left end of an array that C<pop()> and C<push()> do to the
|
|
right end.
|
|
|
|
=item shmctl ID,CMD,ARG
|
|
|
|
Calls the System V IPC function shmctl. You'll probably have to say
|
|
|
|
use IPC::SysV;
|
|
|
|
first to get the correct constant definitions. If CMD is C<IPC_STAT>,
|
|
then ARG must be a variable which will hold the returned C<shmid_ds>
|
|
structure. Returns like ioctl: the undefined value for error, "C<0> but
|
|
true" for zero, or the actual return value otherwise.
|
|
See also C<IPC::SysV> documentation.
|
|
|
|
=item shmget KEY,SIZE,FLAGS
|
|
|
|
Calls the System V IPC function shmget. Returns the shared memory
|
|
segment id, or the undefined value if there is an error.
|
|
See also C<IPC::SysV> documentation.
|
|
|
|
=item shmread ID,VAR,POS,SIZE
|
|
|
|
=item shmwrite ID,STRING,POS,SIZE
|
|
|
|
Reads or writes the System V shared memory segment ID starting at
|
|
position POS for size SIZE by attaching to it, copying in/out, and
|
|
detaching from it. When reading, VAR must be a variable that will
|
|
hold the data read. When writing, if STRING is too long, only SIZE
|
|
bytes are used; if STRING is too short, nulls are written to fill out
|
|
SIZE bytes. Return TRUE if successful, or FALSE if there is an error.
|
|
See also C<IPC::SysV> documentation and the C<IPC::Shareable> module
|
|
from CPAN.
|
|
|
|
=item shutdown SOCKET,HOW
|
|
|
|
Shuts down a socket connection in the manner indicated by HOW, which
|
|
has the same interpretation as in the system call of the same name.
|
|
|
|
shutdown(SOCKET, 0); # I/we have stopped reading data
|
|
shutdown(SOCKET, 1); # I/we have stopped writing data
|
|
shutdown(SOCKET, 2); # I/we have stopped using this socket
|
|
|
|
This is useful with sockets when you want to tell the other
|
|
side you're done writing but not done reading, or vice versa.
|
|
It's also a more insistent form of close because it also
|
|
disables the filedescriptor in any forked copies in other
|
|
processes.
|
|
|
|
=item sin EXPR
|
|
|
|
=item sin
|
|
|
|
Returns the sine of EXPR (expressed in radians). If EXPR is omitted,
|
|
returns sine of C<$_>.
|
|
|
|
For the inverse sine operation, you may use the C<POSIX::asin()>
|
|
function, or use this relation:
|
|
|
|
sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) }
|
|
|
|
=item sleep EXPR
|
|
|
|
=item sleep
|
|
|
|
Causes the script to sleep for EXPR seconds, or forever if no EXPR.
|
|
May be interrupted if the process receives a signal such as C<SIGALRM>.
|
|
Returns the number of seconds actually slept. You probably cannot
|
|
mix C<alarm()> and C<sleep()> calls, because C<sleep()> is often implemented
|
|
using C<alarm()>.
|
|
|
|
On some older systems, it may sleep up to a full second less than what
|
|
you requested, depending on how it counts seconds. Most modern systems
|
|
always sleep the full amount. They may appear to sleep longer than that,
|
|
however, because your process might not be scheduled right away in a
|
|
busy multitasking system.
|
|
|
|
For delays of finer granularity than one second, you may use Perl's
|
|
C<syscall()> interface to access setitimer(2) if your system supports it,
|
|
or else see L</select> above.
|
|
|
|
See also the POSIX module's C<sigpause()> function.
|
|
|
|
=item socket SOCKET,DOMAIN,TYPE,PROTOCOL
|
|
|
|
Opens a socket of the specified kind and attaches it to filehandle
|
|
SOCKET. DOMAIN, TYPE, and PROTOCOL are specified the same as for the
|
|
system call of the same name. You should "C<use Socket;>" first to get
|
|
the proper definitions imported. See the examples in L<perlipc/"Sockets: Client/Server Communication">.
|
|
|
|
=item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL
|
|
|
|
Creates an unnamed pair of sockets in the specified domain, of the
|
|
specified type. DOMAIN, TYPE, and PROTOCOL are specified the same as
|
|
for the system call of the same name. If unimplemented, yields a fatal
|
|
error. Returns TRUE if successful.
|
|
|
|
Some systems defined C<pipe()> in terms of C<socketpair()>, in which a call
|
|
to C<pipe(Rdr, Wtr)> is essentially:
|
|
|
|
use Socket;
|
|
socketpair(Rdr, Wtr, AF_UNIX, SOCK_STREAM, PF_UNSPEC);
|
|
shutdown(Rdr, 1); # no more writing for reader
|
|
shutdown(Wtr, 0); # no more reading for writer
|
|
|
|
See L<perlipc> for an example of socketpair use.
|
|
|
|
=item sort SUBNAME LIST
|
|
|
|
=item sort BLOCK LIST
|
|
|
|
=item sort LIST
|
|
|
|
Sorts the LIST and returns the sorted list value. If SUBNAME or BLOCK
|
|
is omitted, C<sort()>s in standard string comparison order. If SUBNAME is
|
|
specified, it gives the name of a subroutine that returns an integer
|
|
less than, equal to, or greater than C<0>, depending on how the elements
|
|
of the array are to be ordered. (The C<E<lt>=E<gt>> and C<cmp>
|
|
operators are extremely useful in such routines.) SUBNAME may be a
|
|
scalar variable name (unsubscripted), in which case the value provides
|
|
the name of (or a reference to) the actual subroutine to use. In place
|
|
of a SUBNAME, you can provide a BLOCK as an anonymous, in-line sort
|
|
subroutine.
|
|
|
|
In the interests of efficiency the normal calling code for subroutines is
|
|
bypassed, with the following effects: the subroutine may not be a
|
|
recursive subroutine, and the two elements to be compared are passed into
|
|
the subroutine not via C<@_> but as the package global variables C<$a> and
|
|
C<$b> (see example below). They are passed by reference, so don't
|
|
modify C<$a> and C<$b>. And don't try to declare them as lexicals either.
|
|
|
|
You also cannot exit out of the sort block or subroutine using any of the
|
|
loop control operators described in L<perlsyn> or with C<goto()>.
|
|
|
|
When C<use locale> is in effect, C<sort LIST> sorts LIST according to the
|
|
current collation locale. See L<perllocale>.
|
|
|
|
Examples:
|
|
|
|
# sort lexically
|
|
@articles = sort @files;
|
|
|
|
# same thing, but with explicit sort routine
|
|
@articles = sort {$a cmp $b} @files;
|
|
|
|
# now case-insensitively
|
|
@articles = sort {uc($a) cmp uc($b)} @files;
|
|
|
|
# same thing in reversed order
|
|
@articles = sort {$b cmp $a} @files;
|
|
|
|
# sort numerically ascending
|
|
@articles = sort {$a <=> $b} @files;
|
|
|
|
# sort numerically descending
|
|
@articles = sort {$b <=> $a} @files;
|
|
|
|
# sort using explicit subroutine name
|
|
sub byage {
|
|
$age{$a} <=> $age{$b}; # presuming numeric
|
|
}
|
|
@sortedclass = sort byage @class;
|
|
|
|
# this sorts the %age hash by value instead of key
|
|
# using an in-line function
|
|
@eldest = sort { $age{$b} <=> $age{$a} } keys %age;
|
|
|
|
sub backwards { $b cmp $a; }
|
|
@harry = ('dog','cat','x','Cain','Abel');
|
|
@george = ('gone','chased','yz','Punished','Axed');
|
|
print sort @harry;
|
|
# prints AbelCaincatdogx
|
|
print sort backwards @harry;
|
|
# prints xdogcatCainAbel
|
|
print sort @george, 'to', @harry;
|
|
# prints AbelAxedCainPunishedcatchaseddoggonetoxyz
|
|
|
|
# inefficiently sort by descending numeric compare using
|
|
# the first integer after the first = sign, or the
|
|
# whole record case-insensitively otherwise
|
|
|
|
@new = sort {
|
|
($b =~ /=(\d+)/)[0] <=> ($a =~ /=(\d+)/)[0]
|
|
||
|
|
uc($a) cmp uc($b)
|
|
} @old;
|
|
|
|
# same thing, but much more efficiently;
|
|
# we'll build auxiliary indices instead
|
|
# for speed
|
|
@nums = @caps = ();
|
|
for (@old) {
|
|
push @nums, /=(\d+)/;
|
|
push @caps, uc($_);
|
|
}
|
|
|
|
@new = @old[ sort {
|
|
$nums[$b] <=> $nums[$a]
|
|
||
|
|
$caps[$a] cmp $caps[$b]
|
|
} 0..$#old
|
|
];
|
|
|
|
# same thing using a Schwartzian Transform (no temps)
|
|
@new = map { $_->[0] }
|
|
sort { $b->[1] <=> $a->[1]
|
|
||
|
|
$a->[2] cmp $b->[2]
|
|
} map { [$_, /=(\d+)/, uc($_)] } @old;
|
|
|
|
If you're using strict, you I<MUST NOT> declare C<$a>
|
|
and C<$b> as lexicals. They are package globals. That means
|
|
if you're in the C<main> package, it's
|
|
|
|
@articles = sort {$main::b <=> $main::a} @files;
|
|
|
|
or just
|
|
|
|
@articles = sort {$::b <=> $::a} @files;
|
|
|
|
but if you're in the C<FooPack> package, it's
|
|
|
|
@articles = sort {$FooPack::b <=> $FooPack::a} @files;
|
|
|
|
The comparison function is required to behave. If it returns
|
|
inconsistent results (sometimes saying C<$x[1]> is less than C<$x[2]> and
|
|
sometimes saying the opposite, for example) the results are not
|
|
well-defined.
|
|
|
|
=item splice ARRAY,OFFSET,LENGTH,LIST
|
|
|
|
=item splice ARRAY,OFFSET,LENGTH
|
|
|
|
=item splice ARRAY,OFFSET
|
|
|
|
Removes the elements designated by OFFSET and LENGTH from an array, and
|
|
replaces them with the elements of LIST, if any. In list context,
|
|
returns the elements removed from the array. In scalar context,
|
|
returns the last element removed, or C<undef> if no elements are
|
|
removed. The array grows or shrinks as necessary.
|
|
If OFFSET is negative then it start that far from the end of the array.
|
|
If LENGTH is omitted, removes everything from OFFSET onward.
|
|
If LENGTH is negative, leave that many elements off the end of the array.
|
|
The following equivalences hold (assuming C<$[ == 0>):
|
|
|
|
push(@a,$x,$y) splice(@a,@a,0,$x,$y)
|
|
pop(@a) splice(@a,-1)
|
|
shift(@a) splice(@a,0,1)
|
|
unshift(@a,$x,$y) splice(@a,0,0,$x,$y)
|
|
$a[$x] = $y splice(@a,$x,1,$y)
|
|
|
|
Example, assuming array lengths are passed before arrays:
|
|
|
|
sub aeq { # compare two list values
|
|
my(@a) = splice(@_,0,shift);
|
|
my(@b) = splice(@_,0,shift);
|
|
return 0 unless @a == @b; # same len?
|
|
while (@a) {
|
|
return 0 if pop(@a) ne pop(@b);
|
|
}
|
|
return 1;
|
|
}
|
|
if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... }
|
|
|
|
=item split /PATTERN/,EXPR,LIMIT
|
|
|
|
=item split /PATTERN/,EXPR
|
|
|
|
=item split /PATTERN/
|
|
|
|
=item split
|
|
|
|
Splits a string into an array of strings, and returns it. By default,
|
|
empty leading fields are preserved, and empty trailing ones are deleted.
|
|
|
|
If not in list context, returns the number of fields found and splits into
|
|
the C<@_> array. (In list context, you can force the split into C<@_> by
|
|
using C<??> as the pattern delimiters, but it still returns the list
|
|
value.) The use of implicit split to C<@_> is deprecated, however, because
|
|
it clobbers your subroutine arguments.
|
|
|
|
If EXPR is omitted, splits the C<$_> string. If PATTERN is also omitted,
|
|
splits on whitespace (after skipping any leading whitespace). Anything
|
|
matching PATTERN is taken to be a delimiter separating the fields. (Note
|
|
that the delimiter may be longer than one character.)
|
|
|
|
If LIMIT is specified and positive, splits into no more than that
|
|
many fields (though it may split into fewer). If LIMIT is unspecified
|
|
or zero, trailing null fields are stripped (which potential users
|
|
of C<pop()> would do well to remember). If LIMIT is negative, it is
|
|
treated as if an arbitrarily large LIMIT had been specified.
|
|
|
|
A pattern matching the null string (not to be confused with
|
|
a null pattern C<//>, which is just one member of the set of patterns
|
|
matching a null string) will split the value of EXPR into separate
|
|
characters at each point it matches that way. For example:
|
|
|
|
print join(':', split(/ */, 'hi there'));
|
|
|
|
produces the output 'h:i:t:h:e:r:e'.
|
|
|
|
The LIMIT parameter can be used to split a line partially
|
|
|
|
($login, $passwd, $remainder) = split(/:/, $_, 3);
|
|
|
|
When assigning to a list, if LIMIT is omitted, Perl supplies a LIMIT
|
|
one larger than the number of variables in the list, to avoid
|
|
unnecessary work. For the list above LIMIT would have been 4 by
|
|
default. In time critical applications it behooves you not to split
|
|
into more fields than you really need.
|
|
|
|
If the PATTERN contains parentheses, additional array elements are
|
|
created from each matching substring in the delimiter.
|
|
|
|
split(/([,-])/, "1-10,20", 3);
|
|
|
|
produces the list value
|
|
|
|
(1, '-', 10, ',', 20)
|
|
|
|
If you had the entire header of a normal Unix email message in C<$header>,
|
|
you could split it up into fields and their values this way:
|
|
|
|
$header =~ s/\n\s+/ /g; # fix continuation lines
|
|
%hdrs = (UNIX_FROM => split /^(\S*?):\s*/m, $header);
|
|
|
|
The pattern C</PATTERN/> may be replaced with an expression to specify
|
|
patterns that vary at runtime. (To do runtime compilation only once,
|
|
use C</$variable/o>.)
|
|
|
|
As a special case, specifying a PATTERN of space (C<' '>) will split on
|
|
white space just as C<split()> with no arguments does. Thus, C<split(' ')> can
|
|
be used to emulate B<awk>'s default behavior, whereas C<split(/ /)>
|
|
will give you as many null initial fields as there are leading spaces.
|
|
A C<split()> on C</\s+/> is like a C<split(' ')> except that any leading
|
|
whitespace produces a null first field. A C<split()> with no arguments
|
|
really does a C<split(' ', $_)> internally.
|
|
|
|
Example:
|
|
|
|
open(PASSWD, '/etc/passwd');
|
|
while (<PASSWD>) {
|
|
($login, $passwd, $uid, $gid,
|
|
$gcos, $home, $shell) = split(/:/);
|
|
#...
|
|
}
|
|
|
|
(Note that C<$shell> above will still have a newline on it. See L</chop>,
|
|
L</chomp>, and L</join>.)
|
|
|
|
=item sprintf FORMAT, LIST
|
|
|
|
Returns a string formatted by the usual C<printf()> conventions of the
|
|
C library function C<sprintf()>. See L<sprintf(3)> or L<printf(3)>
|
|
on your system for an explanation of the general principles.
|
|
|
|
Perl does its own C<sprintf()> formatting -- it emulates the C
|
|
function C<sprintf()>, but it doesn't use it (except for floating-point
|
|
numbers, and even then only the standard modifiers are allowed). As a
|
|
result, any non-standard extensions in your local C<sprintf()> are not
|
|
available from Perl.
|
|
|
|
Perl's C<sprintf()> permits the following universally-known conversions:
|
|
|
|
%% a percent sign
|
|
%c a character with the given number
|
|
%s a string
|
|
%d a signed integer, in decimal
|
|
%u an unsigned integer, in decimal
|
|
%o an unsigned integer, in octal
|
|
%x an unsigned integer, in hexadecimal
|
|
%e a floating-point number, in scientific notation
|
|
%f a floating-point number, in fixed decimal notation
|
|
%g a floating-point number, in %e or %f notation
|
|
|
|
In addition, Perl permits the following widely-supported conversions:
|
|
|
|
%X like %x, but using upper-case letters
|
|
%E like %e, but using an upper-case "E"
|
|
%G like %g, but with an upper-case "E" (if applicable)
|
|
%p a pointer (outputs the Perl value's address in hexadecimal)
|
|
%n special: *stores* the number of characters output so far
|
|
into the next variable in the parameter list
|
|
|
|
Finally, for backward (and we do mean "backward") compatibility, Perl
|
|
permits these unnecessary but widely-supported conversions:
|
|
|
|
%i a synonym for %d
|
|
%D a synonym for %ld
|
|
%U a synonym for %lu
|
|
%O a synonym for %lo
|
|
%F a synonym for %f
|
|
|
|
Perl permits the following universally-known flags between the C<%>
|
|
and the conversion letter:
|
|
|
|
space prefix positive number with a space
|
|
+ prefix positive number with a plus sign
|
|
- left-justify within the field
|
|
0 use zeros, not spaces, to right-justify
|
|
# prefix non-zero octal with "0", non-zero hex with "0x"
|
|
number minimum field width
|
|
.number "precision": digits after decimal point for
|
|
floating-point, max length for string, minimum length
|
|
for integer
|
|
l interpret integer as C type "long" or "unsigned long"
|
|
h interpret integer as C type "short" or "unsigned short"
|
|
|
|
There is also one Perl-specific flag:
|
|
|
|
V interpret integer as Perl's standard integer type
|
|
|
|
Where a number would appear in the flags, an asterisk ("C<*>") may be
|
|
used instead, in which case Perl uses the next item in the parameter
|
|
list as the given number (that is, as the field width or precision).
|
|
If a field width obtained through "C<*>" is negative, it has the same
|
|
effect as the "C<->" flag: left-justification.
|
|
|
|
If C<use locale> is in effect, the character used for the decimal
|
|
point in formatted real numbers is affected by the LC_NUMERIC locale.
|
|
See L<perllocale>.
|
|
|
|
=item sqrt EXPR
|
|
|
|
=item sqrt
|
|
|
|
Return the square root of EXPR. If EXPR is omitted, returns square
|
|
root of C<$_>. Only works on non-negative operands, unless you've
|
|
loaded the standard Math::Complex module.
|
|
|
|
use Math::Complex;
|
|
print sqrt(-2); # prints 1.4142135623731i
|
|
|
|
=item srand EXPR
|
|
|
|
=item srand
|
|
|
|
Sets the random number seed for the C<rand()> operator. If EXPR is
|
|
omitted, uses a semi-random value supplied by the kernel (if it supports
|
|
the F</dev/urandom> device) or based on the current time and process
|
|
ID, among other things. In versions of Perl prior to 5.004 the default
|
|
seed was just the current C<time()>. This isn't a particularly good seed,
|
|
so many old programs supply their own seed value (often C<time ^ $$> or
|
|
C<time ^ ($$ + ($$ E<lt>E<lt> 15))>), but that isn't necessary any more.
|
|
|
|
In fact, it's usually not necessary to call C<srand()> at all, because if
|
|
it is not called explicitly, it is called implicitly at the first use of
|
|
the C<rand()> operator. However, this was not the case in version of Perl
|
|
before 5.004, so if your script will run under older Perl versions, it
|
|
should call C<srand()>.
|
|
|
|
Note that you need something much more random than the default seed for
|
|
cryptographic purposes. Checksumming the compressed output of one or more
|
|
rapidly changing operating system status programs is the usual method. For
|
|
example:
|
|
|
|
srand (time ^ $$ ^ unpack "%L*", `ps axww | gzip`);
|
|
|
|
If you're particularly concerned with this, see the C<Math::TrulyRandom>
|
|
module in CPAN.
|
|
|
|
Do I<not> call C<srand()> multiple times in your program unless you know
|
|
exactly what you're doing and why you're doing it. The point of the
|
|
function is to "seed" the C<rand()> function so that C<rand()> can produce
|
|
a different sequence each time you run your program. Just do it once at the
|
|
top of your program, or you I<won't> get random numbers out of C<rand()>!
|
|
|
|
Frequently called programs (like CGI scripts) that simply use
|
|
|
|
time ^ $$
|
|
|
|
for a seed can fall prey to the mathematical property that
|
|
|
|
a^b == (a+1)^(b+1)
|
|
|
|
one-third of the time. So don't do that.
|
|
|
|
=item stat FILEHANDLE
|
|
|
|
=item stat EXPR
|
|
|
|
=item stat
|
|
|
|
Returns a 13-element list giving the status info for a file, either
|
|
the file opened via FILEHANDLE, or named by EXPR. If EXPR is omitted,
|
|
it stats C<$_>. Returns a null list if the stat fails. Typically used
|
|
as follows:
|
|
|
|
($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
|
|
$atime,$mtime,$ctime,$blksize,$blocks)
|
|
= stat($filename);
|
|
|
|
Not all fields are supported on all filesystem types. Here are the
|
|
meaning of the fields:
|
|
|
|
0 dev device number of filesystem
|
|
1 ino inode number
|
|
2 mode file mode (type and permissions)
|
|
3 nlink number of (hard) links to the file
|
|
4 uid numeric user ID of file's owner
|
|
5 gid numeric group ID of file's owner
|
|
6 rdev the device identifier (special files only)
|
|
7 size total size of file, in bytes
|
|
8 atime last access time since the epoch
|
|
9 mtime last modify time since the epoch
|
|
10 ctime inode change time (NOT creation time!) since the epoch
|
|
11 blksize preferred block size for file system I/O
|
|
12 blocks actual number of blocks allocated
|
|
|
|
(The epoch was at 00:00 January 1, 1970 GMT.)
|
|
|
|
If stat is passed the special filehandle consisting of an underline, no
|
|
stat is done, but the current contents of the stat structure from the
|
|
last stat or filetest are returned. Example:
|
|
|
|
if (-x $file && (($d) = stat(_)) && $d < 0) {
|
|
print "$file is executable NFS file\n";
|
|
}
|
|
|
|
(This works on machines only for which the device number is negative under NFS.)
|
|
|
|
Because the mode contains both the file type and its permissions, you
|
|
should mask off the file type portion and (s)printf using a C<"%o">
|
|
if you want to see the real permissions.
|
|
|
|
$mode = (stat($filename))[2];
|
|
printf "Permissions are %04o\n", $mode & 07777;
|
|
|
|
|
|
In scalar context, C<stat()> returns a boolean value indicating success
|
|
or failure, and, if successful, sets the information associated with
|
|
the special filehandle C<_>.
|
|
|
|
The File::stat module provides a convenient, by-name access mechanism:
|
|
|
|
use File::stat;
|
|
$sb = stat($filename);
|
|
printf "File is %s, size is %s, perm %04o, mtime %s\n",
|
|
$filename, $sb->size, $sb->mode & 07777,
|
|
scalar localtime $sb->mtime;
|
|
|
|
=item study SCALAR
|
|
|
|
=item study
|
|
|
|
Takes extra time to study SCALAR (C<$_> if unspecified) in anticipation of
|
|
doing many pattern matches on the string before it is next modified.
|
|
This may or may not save time, depending on the nature and number of
|
|
patterns you are searching on, and on the distribution of character
|
|
frequencies in the string to be searched -- you probably want to compare
|
|
run times with and without it to see which runs faster. Those loops
|
|
which scan for many short constant strings (including the constant
|
|
parts of more complex patterns) will benefit most. You may have only
|
|
one C<study()> active at a time -- if you study a different scalar the first
|
|
is "unstudied". (The way C<study()> works is this: a linked list of every
|
|
character in the string to be searched is made, so we know, for
|
|
example, where all the C<'k'> characters are. From each search string,
|
|
the rarest character is selected, based on some static frequency tables
|
|
constructed from some C programs and English text. Only those places
|
|
that contain this "rarest" character are examined.)
|
|
|
|
For example, here is a loop that inserts index producing entries
|
|
before any line containing a certain pattern:
|
|
|
|
while (<>) {
|
|
study;
|
|
print ".IX foo\n" if /\bfoo\b/;
|
|
print ".IX bar\n" if /\bbar\b/;
|
|
print ".IX blurfl\n" if /\bblurfl\b/;
|
|
# ...
|
|
print;
|
|
}
|
|
|
|
In searching for C</\bfoo\b/>, only those locations in C<$_> that contain C<"f">
|
|
will be looked at, because C<"f"> is rarer than C<"o">. In general, this is
|
|
a big win except in pathological cases. The only question is whether
|
|
it saves you more time than it took to build the linked list in the
|
|
first place.
|
|
|
|
Note that if you have to look for strings that you don't know till
|
|
runtime, you can build an entire loop as a string and C<eval()> that to
|
|
avoid recompiling all your patterns all the time. Together with
|
|
undefining C<$/> to input entire files as one record, this can be very
|
|
fast, often faster than specialized programs like fgrep(1). The following
|
|
scans a list of files (C<@files>) for a list of words (C<@words>), and prints
|
|
out the names of those files that contain a match:
|
|
|
|
$search = 'while (<>) { study;';
|
|
foreach $word (@words) {
|
|
$search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n";
|
|
}
|
|
$search .= "}";
|
|
@ARGV = @files;
|
|
undef $/;
|
|
eval $search; # this screams
|
|
$/ = "\n"; # put back to normal input delimiter
|
|
foreach $file (sort keys(%seen)) {
|
|
print $file, "\n";
|
|
}
|
|
|
|
=item sub BLOCK
|
|
|
|
=item sub NAME
|
|
|
|
=item sub NAME BLOCK
|
|
|
|
This is subroutine definition, not a real function I<per se>. With just a
|
|
NAME (and possibly prototypes), it's just a forward declaration. Without
|
|
a NAME, it's an anonymous function declaration, and does actually return a
|
|
value: the CODE ref of the closure you just created. See L<perlsub> and
|
|
L<perlref> for details.
|
|
|
|
=item substr EXPR,OFFSET,LEN,REPLACEMENT
|
|
|
|
=item substr EXPR,OFFSET,LEN
|
|
|
|
=item substr EXPR,OFFSET
|
|
|
|
Extracts a substring out of EXPR and returns it. First character is at
|
|
offset C<0>, or whatever you've set C<$[> to (but don't do that).
|
|
If OFFSET is negative (or more precisely, less than C<$[>), starts
|
|
that far from the end of the string. If LEN is omitted, returns
|
|
everything to the end of the string. If LEN is negative, leaves that
|
|
many characters off the end of the string.
|
|
|
|
If you specify a substring that is partly outside the string, the part
|
|
within the string is returned. If the substring is totally outside
|
|
the string a warning is produced.
|
|
|
|
You can use the substr() function as an lvalue, in which case EXPR
|
|
must itself be an lvalue. If you assign something shorter than LEN,
|
|
the string will shrink, and if you assign something longer than LEN,
|
|
the string will grow to accommodate it. To keep the string the same
|
|
length you may need to pad or chop your value using C<sprintf()>.
|
|
|
|
An alternative to using substr() as an lvalue is to specify the
|
|
replacement string as the 4th argument. This allows you to replace
|
|
parts of the EXPR and return what was there before in one operation,
|
|
just as you can with splice().
|
|
|
|
=item symlink OLDFILE,NEWFILE
|
|
|
|
Creates a new filename symbolically linked to the old filename.
|
|
Returns C<1> for success, C<0> otherwise. On systems that don't support
|
|
symbolic links, produces a fatal error at run time. To check for that,
|
|
use eval:
|
|
|
|
$symlink_exists = eval { symlink("",""); 1 };
|
|
|
|
=item syscall LIST
|
|
|
|
Calls the system call specified as the first element of the list,
|
|
passing the remaining elements as arguments to the system call. If
|
|
unimplemented, produces a fatal error. The arguments are interpreted
|
|
as follows: if a given argument is numeric, the argument is passed as
|
|
an int. If not, the pointer to the string value is passed. You are
|
|
responsible to make sure a string is pre-extended long enough to
|
|
receive any result that might be written into a string. You can't use a
|
|
string literal (or other read-only string) as an argument to C<syscall()>
|
|
because Perl has to assume that any string pointer might be written
|
|
through. If your
|
|
integer arguments are not literals and have never been interpreted in a
|
|
numeric context, you may need to add C<0> to them to force them to look
|
|
like numbers. This emulates the C<syswrite()> function (or vice versa):
|
|
|
|
require 'syscall.ph'; # may need to run h2ph
|
|
$s = "hi there\n";
|
|
syscall(&SYS_write, fileno(STDOUT), $s, length $s);
|
|
|
|
Note that Perl supports passing of up to only 14 arguments to your system call,
|
|
which in practice should usually suffice.
|
|
|
|
Syscall returns whatever value returned by the system call it calls.
|
|
If the system call fails, C<syscall()> returns C<-1> and sets C<$!> (errno).
|
|
Note that some system calls can legitimately return C<-1>. The proper
|
|
way to handle such calls is to assign C<$!=0;> before the call and
|
|
check the value of C<$!> if syscall returns C<-1>.
|
|
|
|
There's a problem with C<syscall(&SYS_pipe)>: it returns the file
|
|
number of the read end of the pipe it creates. There is no way
|
|
to retrieve the file number of the other end. You can avoid this
|
|
problem by using C<pipe()> instead.
|
|
|
|
=item sysopen FILEHANDLE,FILENAME,MODE
|
|
|
|
=item sysopen FILEHANDLE,FILENAME,MODE,PERMS
|
|
|
|
Opens the file whose filename is given by FILENAME, and associates it
|
|
with FILEHANDLE. If FILEHANDLE is an expression, its value is used as
|
|
the name of the real filehandle wanted. This function calls the
|
|
underlying operating system's C<open()> function with the parameters
|
|
FILENAME, MODE, PERMS.
|
|
|
|
The possible values and flag bits of the MODE parameter are
|
|
system-dependent; they are available via the standard module C<Fcntl>.
|
|
For historical reasons, some values work on almost every system
|
|
supported by perl: zero means read-only, one means write-only, and two
|
|
means read/write. We know that these values do I<not> work under
|
|
OS/390 & VM/ESA Unix and on the Macintosh; you probably don't want to
|
|
use them in new code.
|
|
|
|
If the file named by FILENAME does not exist and the C<open()> call creates
|
|
it (typically because MODE includes the C<O_CREAT> flag), then the value of
|
|
PERMS specifies the permissions of the newly created file. If you omit
|
|
the PERMS argument to C<sysopen()>, Perl uses the octal value C<0666>.
|
|
These permission values need to be in octal, and are modified by your
|
|
process's current C<umask>.
|
|
|
|
You should seldom if ever use C<0644> as argument to C<sysopen()>, because
|
|
that takes away the user's option to have a more permissive umask.
|
|
Better to omit it. See the perlfunc(1) entry on C<umask> for more
|
|
on this.
|
|
|
|
See L<perlopentut> for a kinder, gentler explanation of opening files.
|
|
|
|
=item sysread FILEHANDLE,SCALAR,LENGTH,OFFSET
|
|
|
|
=item sysread FILEHANDLE,SCALAR,LENGTH
|
|
|
|
Attempts to read LENGTH bytes of data into variable SCALAR from the
|
|
specified FILEHANDLE, using the system call read(2). It bypasses stdio,
|
|
so mixing this with other kinds of reads, C<print()>, C<write()>,
|
|
C<seek()>, C<tell()>, or C<eof()> can cause confusion because stdio
|
|
usually buffers data. Returns the number of bytes actually read, C<0>
|
|
at end of file, or undef if there was an error. SCALAR will be grown or
|
|
shrunk so that the last byte actually read is the last byte of the
|
|
scalar after the read.
|
|
|
|
An OFFSET may be specified to place the read data at some place in the
|
|
string other than the beginning. A negative OFFSET specifies
|
|
placement at that many bytes counting backwards from the end of the
|
|
string. A positive OFFSET greater than the length of SCALAR results
|
|
in the string being padded to the required size with C<"\0"> bytes before
|
|
the result of the read is appended.
|
|
|
|
There is no syseof() function, which is ok, since eof() doesn't work
|
|
very well on device files (like ttys) anyway. Use sysread() and check
|
|
for a return value for 0 to decide whether you're done.
|
|
|
|
=item sysseek FILEHANDLE,POSITION,WHENCE
|
|
|
|
Sets FILEHANDLE's system position using the system call lseek(2). It
|
|
bypasses stdio, so mixing this with reads (other than C<sysread()>),
|
|
C<print()>, C<write()>, C<seek()>, C<tell()>, or C<eof()> may cause
|
|
confusion. FILEHANDLE may be an expression whose value gives the name
|
|
of the filehandle. The values for WHENCE are C<0> to set the new
|
|
position to POSITION, C<1> to set the it to the current position plus
|
|
POSITION, and C<2> to set it to EOF plus POSITION (typically negative).
|
|
For WHENCE, you may use the constants C<SEEK_SET>, C<SEEK_CUR>, and
|
|
C<SEEK_END> from either the C<IO::Seekable> or the POSIX module.
|
|
|
|
Returns the new position, or the undefined value on failure. A position
|
|
of zero is returned as the string "C<0> but true"; thus C<sysseek()> returns
|
|
TRUE on success and FALSE on failure, yet you can still easily determine
|
|
the new position.
|
|
|
|
=item system LIST
|
|
|
|
=item system PROGRAM LIST
|
|
|
|
Does exactly the same thing as "C<exec LIST>", except that a fork is done
|
|
first, and the parent process waits for the child process to complete.
|
|
Note that argument processing varies depending on the number of
|
|
arguments. If there is more than one argument in LIST, or if LIST is
|
|
an array with more than one value, starts the program given by the
|
|
first element of the list with arguments given by the rest of the list.
|
|
If there is only one scalar argument, the argument is
|
|
checked for shell metacharacters, and if there are any, the entire
|
|
argument is passed to the system's command shell for parsing (this is
|
|
C</bin/sh -c> on Unix platforms, but varies on other platforms). If
|
|
there are no shell metacharacters in the argument, it is split into
|
|
words and passed directly to C<execvp()>, which is more efficient.
|
|
|
|
The return value is the exit status of the program as
|
|
returned by the C<wait()> call. To get the actual exit value divide by
|
|
256. See also L</exec>. This is I<NOT> what you want to use to capture
|
|
the output from a command, for that you should use merely backticks or
|
|
C<qx//>, as described in L<perlop/"`STRING`">.
|
|
|
|
Like C<exec()>, C<system()> allows you to lie to a program about its name if
|
|
you use the "C<system PROGRAM LIST>" syntax. Again, see L</exec>.
|
|
|
|
Because C<system()> and backticks block C<SIGINT> and C<SIGQUIT>, killing the
|
|
program they're running doesn't actually interrupt your program.
|
|
|
|
@args = ("command", "arg1", "arg2");
|
|
system(@args) == 0
|
|
or die "system @args failed: $?"
|
|
|
|
You can check all the failure possibilities by inspecting
|
|
C<$?> like this:
|
|
|
|
$exit_value = $? >> 8;
|
|
$signal_num = $? & 127;
|
|
$dumped_core = $? & 128;
|
|
|
|
When the arguments get executed via the system shell, results
|
|
and return codes will be subject to its quirks and capabilities.
|
|
See L<perlop/"`STRING`"> and L</exec> for details.
|
|
|
|
=item syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET
|
|
|
|
=item syswrite FILEHANDLE,SCALAR,LENGTH
|
|
|
|
=item syswrite FILEHANDLE,SCALAR
|
|
|
|
Attempts to write LENGTH bytes of data from variable SCALAR to the
|
|
specified FILEHANDLE, using the system call write(2). If LENGTH is
|
|
not specified, writes whole SCALAR. It bypasses
|
|
stdio, so mixing this with reads (other than C<sysread())>, C<print()>,
|
|
C<write()>, C<seek()>, C<tell()>, or C<eof()> may cause confusion
|
|
because stdio usually buffers data. Returns the number of bytes
|
|
actually written, or C<undef> if there was an error. If the LENGTH is
|
|
greater than the available data in the SCALAR after the OFFSET, only as
|
|
much data as is available will be written.
|
|
|
|
An OFFSET may be specified to write the data from some part of the
|
|
string other than the beginning. A negative OFFSET specifies writing
|
|
that many bytes counting backwards from the end of the string. In the
|
|
case the SCALAR is empty you can use OFFSET but only zero offset.
|
|
|
|
=item tell FILEHANDLE
|
|
|
|
=item tell
|
|
|
|
Returns the current position for FILEHANDLE. FILEHANDLE may be an
|
|
expression whose value gives the name of the actual filehandle. If
|
|
FILEHANDLE is omitted, assumes the file last read.
|
|
|
|
There is no C<systell()> function. Use C<sysseek(FH, 0, 1)> for that.
|
|
|
|
=item telldir DIRHANDLE
|
|
|
|
Returns the current position of the C<readdir()> routines on DIRHANDLE.
|
|
Value may be given to C<seekdir()> to access a particular location in a
|
|
directory. Has the same caveats about possible directory compaction as
|
|
the corresponding system library routine.
|
|
|
|
=item tie VARIABLE,CLASSNAME,LIST
|
|
|
|
This function binds a variable to a package class that will provide the
|
|
implementation for the variable. VARIABLE is the name of the variable
|
|
to be enchanted. CLASSNAME is the name of a class implementing objects
|
|
of correct type. Any additional arguments are passed to the "C<new()>"
|
|
method of the class (meaning C<TIESCALAR>, C<TIEHANDLE>, C<TIEARRAY>,
|
|
or C<TIEHASH>). Typically these are arguments such as might be passed
|
|
to the C<dbm_open()> function of C. The object returned by the "C<new()>"
|
|
method is also returned by the C<tie()> function, which would be useful
|
|
if you want to access other methods in CLASSNAME.
|
|
|
|
Note that functions such as C<keys()> and C<values()> may return huge lists
|
|
when used on large objects, like DBM files. You may prefer to use the
|
|
C<each()> function to iterate over such. Example:
|
|
|
|
# print out history file offsets
|
|
use NDBM_File;
|
|
tie(%HIST, 'NDBM_File', '/usr/lib/news/history', 1, 0);
|
|
while (($key,$val) = each %HIST) {
|
|
print $key, ' = ', unpack('L',$val), "\n";
|
|
}
|
|
untie(%HIST);
|
|
|
|
A class implementing a hash should have the following methods:
|
|
|
|
TIEHASH classname, LIST
|
|
FETCH this, key
|
|
STORE this, key, value
|
|
DELETE this, key
|
|
CLEAR this
|
|
EXISTS this, key
|
|
FIRSTKEY this
|
|
NEXTKEY this, lastkey
|
|
DESTROY this
|
|
|
|
A class implementing an ordinary array should have the following methods:
|
|
|
|
TIEARRAY classname, LIST
|
|
FETCH this, key
|
|
STORE this, key, value
|
|
FETCHSIZE this
|
|
STORESIZE this, count
|
|
CLEAR this
|
|
PUSH this, LIST
|
|
POP this
|
|
SHIFT this
|
|
UNSHIFT this, LIST
|
|
SPLICE this, offset, length, LIST
|
|
EXTEND this, count
|
|
DESTROY this
|
|
|
|
A class implementing a file handle should have the following methods:
|
|
|
|
TIEHANDLE classname, LIST
|
|
READ this, scalar, length, offset
|
|
READLINE this
|
|
GETC this
|
|
WRITE this, scalar, length, offset
|
|
PRINT this, LIST
|
|
PRINTF this, format, LIST
|
|
CLOSE this
|
|
DESTROY this
|
|
|
|
A class implementing a scalar should have the following methods:
|
|
|
|
TIESCALAR classname, LIST
|
|
FETCH this,
|
|
STORE this, value
|
|
DESTROY this
|
|
|
|
Not all methods indicated above need be implemented. See L<perltie>,
|
|
L<Tie::Hash>, L<Tie::Array>, L<Tie::Scalar>, and L<Tie::Handle>.
|
|
|
|
Unlike C<dbmopen()>, the C<tie()> function will not use or require a module
|
|
for you--you need to do that explicitly yourself. See L<DB_File>
|
|
or the F<Config> module for interesting C<tie()> implementations.
|
|
|
|
For further details see L<perltie>, L<"tied VARIABLE">.
|
|
|
|
=item tied VARIABLE
|
|
|
|
Returns a reference to the object underlying VARIABLE (the same value
|
|
that was originally returned by the C<tie()> call that bound the variable
|
|
to a package.) Returns the undefined value if VARIABLE isn't tied to a
|
|
package.
|
|
|
|
=item time
|
|
|
|
Returns the number of non-leap seconds since whatever time the system
|
|
considers to be the epoch (that's 00:00:00, January 1, 1904 for MacOS,
|
|
and 00:00:00 UTC, January 1, 1970 for most other systems).
|
|
Suitable for feeding to C<gmtime()> and C<localtime()>.
|
|
|
|
=item times
|
|
|
|
Returns a four-element list giving the user and system times, in
|
|
seconds, for this process and the children of this process.
|
|
|
|
($user,$system,$cuser,$csystem) = times;
|
|
|
|
=item tr///
|
|
|
|
The transliteration operator. Same as C<y///>. See L<perlop>.
|
|
|
|
=item truncate FILEHANDLE,LENGTH
|
|
|
|
=item truncate EXPR,LENGTH
|
|
|
|
Truncates the file opened on FILEHANDLE, or named by EXPR, to the
|
|
specified length. Produces a fatal error if truncate isn't implemented
|
|
on your system. Returns TRUE if successful, the undefined value
|
|
otherwise.
|
|
|
|
=item uc EXPR
|
|
|
|
=item uc
|
|
|
|
Returns an uppercased version of EXPR. This is the internal function
|
|
implementing the C<\U> escape in double-quoted strings.
|
|
Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>.
|
|
(It does not attempt to do titlecase mapping on initial letters. See C<ucfirst()> for that.)
|
|
|
|
If EXPR is omitted, uses C<$_>.
|
|
|
|
=item ucfirst EXPR
|
|
|
|
=item ucfirst
|
|
|
|
Returns the value of EXPR with the first character in uppercase. This is
|
|
the internal function implementing the C<\u> escape in double-quoted strings.
|
|
Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>.
|
|
|
|
If EXPR is omitted, uses C<$_>.
|
|
|
|
=item umask EXPR
|
|
|
|
=item umask
|
|
|
|
Sets the umask for the process to EXPR and returns the previous value.
|
|
If EXPR is omitted, merely returns the current umask.
|
|
|
|
The Unix permission C<rwxr-x---> is represented as three sets of three
|
|
bits, or three octal digits: C<0750> (the leading 0 indicates octal
|
|
and isn't one of the digits). The C<umask> value is such a number
|
|
representing disabled permissions bits. The permission (or "mode")
|
|
values you pass C<mkdir> or C<sysopen> are modified by your umask, so
|
|
even if you tell C<sysopen> to create a file with permissions C<0777>,
|
|
if your umask is C<0022> then the file will actually be created with
|
|
permissions C<0755>. If your C<umask> were C<0027> (group can't
|
|
write; others can't read, write, or execute), then passing
|
|
C<sysopen()> C<0666> would create a file with mode C<0640> (C<0666 &~
|
|
027> is C<0640>).
|
|
|
|
Here's some advice: supply a creation mode of C<0666> for regular
|
|
files (in C<sysopen()>) and one of C<0777> for directories (in
|
|
C<mkdir()>) and executable files. This gives users the freedom of
|
|
choice: if they want protected files, they might choose process umasks
|
|
of C<022>, C<027>, or even the particularly antisocial mask of C<077>.
|
|
Programs should rarely if ever make policy decisions better left to
|
|
the user. The exception to this is when writing files that should be
|
|
kept private: mail files, web browser cookies, I<.rhosts> files, and
|
|
so on.
|
|
|
|
If umask(2) is not implemented on your system and you are trying to
|
|
restrict access for I<yourself> (i.e., (EXPR & 0700) > 0), produces a
|
|
fatal error at run time. If umask(2) is not implemented and you are
|
|
not trying to restrict access for yourself, returns C<undef>.
|
|
|
|
Remember that a umask is a number, usually given in octal; it is I<not> a
|
|
string of octal digits. See also L</oct>, if all you have is a string.
|
|
|
|
=item undef EXPR
|
|
|
|
=item undef
|
|
|
|
Undefines the value of EXPR, which must be an lvalue. Use only on a
|
|
scalar value, an array (using "C<@>"), a hash (using "C<%>"), a subroutine
|
|
(using "C<&>"), or a typeglob (using "<*>"). (Saying C<undef $hash{$key}>
|
|
will probably not do what you expect on most predefined variables or
|
|
DBM list values, so don't do that; see L<delete>.) Always returns the
|
|
undefined value. You can omit the EXPR, in which case nothing is
|
|
undefined, but you still get an undefined value that you could, for
|
|
instance, return from a subroutine, assign to a variable or pass as a
|
|
parameter. Examples:
|
|
|
|
undef $foo;
|
|
undef $bar{'blurfl'}; # Compare to: delete $bar{'blurfl'};
|
|
undef @ary;
|
|
undef %hash;
|
|
undef &mysub;
|
|
undef *xyz; # destroys $xyz, @xyz, %xyz, &xyz, etc.
|
|
return (wantarray ? (undef, $errmsg) : undef) if $they_blew_it;
|
|
select undef, undef, undef, 0.25;
|
|
($a, $b, undef, $c) = &foo; # Ignore third value returned
|
|
|
|
Note that this is a unary operator, not a list operator.
|
|
|
|
=item unlink LIST
|
|
|
|
=item unlink
|
|
|
|
Deletes a list of files. Returns the number of files successfully
|
|
deleted.
|
|
|
|
$cnt = unlink 'a', 'b', 'c';
|
|
unlink @goners;
|
|
unlink <*.bak>;
|
|
|
|
Note: C<unlink()> will not delete directories unless you are superuser and
|
|
the B<-U> flag is supplied to Perl. Even if these conditions are
|
|
met, be warned that unlinking a directory can inflict damage on your
|
|
filesystem. Use C<rmdir()> instead.
|
|
|
|
If LIST is omitted, uses C<$_>.
|
|
|
|
=item unpack TEMPLATE,EXPR
|
|
|
|
C<Unpack()> does the reverse of C<pack()>: it takes a string representing a
|
|
structure and expands it out into a list value, returning the array
|
|
value. (In scalar context, it returns merely the first value
|
|
produced.) The TEMPLATE has the same format as in the C<pack()> function.
|
|
Here's a subroutine that does substring:
|
|
|
|
sub substr {
|
|
my($what,$where,$howmuch) = @_;
|
|
unpack("x$where a$howmuch", $what);
|
|
}
|
|
|
|
and then there's
|
|
|
|
sub ordinal { unpack("c",$_[0]); } # same as ord()
|
|
|
|
In addition, you may prefix a field with a %E<lt>numberE<gt> to indicate that
|
|
you want a E<lt>numberE<gt>-bit checksum of the items instead of the items
|
|
themselves. Default is a 16-bit checksum. For example, the following
|
|
computes the same number as the System V sum program:
|
|
|
|
while (<>) {
|
|
$checksum += unpack("%32C*", $_);
|
|
}
|
|
$checksum %= 65535;
|
|
|
|
The following efficiently counts the number of set bits in a bit vector:
|
|
|
|
$setbits = unpack("%32b*", $selectmask);
|
|
|
|
See L</pack> for more examples.
|
|
|
|
=item untie VARIABLE
|
|
|
|
Breaks the binding between a variable and a package. (See C<tie()>.)
|
|
|
|
=item unshift ARRAY,LIST
|
|
|
|
Does the opposite of a C<shift()>. Or the opposite of a C<push()>,
|
|
depending on how you look at it. Prepends list to the front of the
|
|
array, and returns the new number of elements in the array.
|
|
|
|
unshift(ARGV, '-e') unless $ARGV[0] =~ /^-/;
|
|
|
|
Note the LIST is prepended whole, not one element at a time, so the
|
|
prepended elements stay in the same order. Use C<reverse()> to do the
|
|
reverse.
|
|
|
|
=item use Module LIST
|
|
|
|
=item use Module
|
|
|
|
=item use Module VERSION LIST
|
|
|
|
=item use VERSION
|
|
|
|
Imports some semantics into the current package from the named module,
|
|
generally by aliasing certain subroutine or variable names into your
|
|
package. It is exactly equivalent to
|
|
|
|
BEGIN { require Module; import Module LIST; }
|
|
|
|
except that Module I<must> be a bareword.
|
|
|
|
If the first argument to C<use> is a number, it is treated as a version
|
|
number instead of a module name. If the version of the Perl interpreter
|
|
is less than VERSION, then an error message is printed and Perl exits
|
|
immediately. This is often useful if you need to check the current
|
|
Perl version before C<use>ing library modules that have changed in
|
|
incompatible ways from older versions of Perl. (We try not to do
|
|
this more than we have to.)
|
|
|
|
The C<BEGIN> forces the C<require> and C<import()> to happen at compile time. The
|
|
C<require> makes sure the module is loaded into memory if it hasn't been
|
|
yet. The C<import()> is not a builtin--it's just an ordinary static method
|
|
call into the "C<Module>" package to tell the module to import the list of
|
|
features back into the current package. The module can implement its
|
|
C<import()> method any way it likes, though most modules just choose to
|
|
derive their C<import()> method via inheritance from the C<Exporter> class that
|
|
is defined in the C<Exporter> module. See L<Exporter>. If no C<import()>
|
|
method can be found then the error is currently silently ignored. This
|
|
may change to a fatal error in a future version.
|
|
|
|
If you don't want your namespace altered, explicitly supply an empty list:
|
|
|
|
use Module ();
|
|
|
|
That is exactly equivalent to
|
|
|
|
BEGIN { require Module }
|
|
|
|
If the VERSION argument is present between Module and LIST, then the
|
|
C<use> will call the VERSION method in class Module with the given
|
|
version as an argument. The default VERSION method, inherited from
|
|
the Universal class, croaks if the given version is larger than the
|
|
value of the variable C<$Module::VERSION>. (Note that there is not a
|
|
comma after VERSION!)
|
|
|
|
Because this is a wide-open interface, pragmas (compiler directives)
|
|
are also implemented this way. Currently implemented pragmas are:
|
|
|
|
use integer;
|
|
use diagnostics;
|
|
use sigtrap qw(SEGV BUS);
|
|
use strict qw(subs vars refs);
|
|
use subs qw(afunc blurfl);
|
|
|
|
Some of these these pseudo-modules import semantics into the current
|
|
block scope (like C<strict> or C<integer>, unlike ordinary modules,
|
|
which import symbols into the current package (which are effective
|
|
through the end of the file).
|
|
|
|
There's a corresponding "C<no>" command that unimports meanings imported
|
|
by C<use>, i.e., it calls C<unimport Module LIST> instead of C<import()>.
|
|
|
|
no integer;
|
|
no strict 'refs';
|
|
|
|
If no C<unimport()> method can be found the call fails with a fatal error.
|
|
|
|
See L<perlmod> for a list of standard modules and pragmas.
|
|
|
|
=item utime LIST
|
|
|
|
Changes the access and modification times on each file of a list of
|
|
files. The first two elements of the list must be the NUMERICAL access
|
|
and modification times, in that order. Returns the number of files
|
|
successfully changed. The inode modification time of each file is set
|
|
to the current time. This code has the same effect as the "C<touch>"
|
|
command if the files already exist:
|
|
|
|
#!/usr/bin/perl
|
|
$now = time;
|
|
utime $now, $now, @ARGV;
|
|
|
|
=item values HASH
|
|
|
|
Returns a list consisting of all the values of the named hash. (In a
|
|
scalar context, returns the number of values.) The values are
|
|
returned in an apparently random order. The actual random order is
|
|
subject to change in future versions of perl, but it is guaranteed to
|
|
be the same order as either the C<keys()> or C<each()> function would
|
|
produce on the same (unmodified) hash.
|
|
|
|
Note that you cannot modify the values of a hash this way, because the
|
|
returned list is just a copy. You need to use a hash slice for that,
|
|
since it's lvaluable in a way that values() is not.
|
|
|
|
for (values %hash) { s/foo/bar/g } # FAILS!
|
|
for (@hash{keys %hash}) { s/foo/bar/g } # ok
|
|
|
|
As a side effect, calling values() resets the HASH's internal iterator.
|
|
See also C<keys()>, C<each()>, and C<sort()>.
|
|
|
|
=item vec EXPR,OFFSET,BITS
|
|
|
|
Treats the string in EXPR as a vector of unsigned integers, and
|
|
returns the value of the bit field specified by OFFSET. BITS specifies
|
|
the number of bits that are reserved for each entry in the bit
|
|
vector. This must be a power of two from 1 to 32. C<vec()> may also be
|
|
assigned to, in which case parentheses are needed to give the expression
|
|
the correct precedence as in
|
|
|
|
vec($image, $max_x * $x + $y, 8) = 3;
|
|
|
|
Vectors created with C<vec()> can also be manipulated with the logical
|
|
operators C<|>, C<&>, and C<^>, which will assume a bit vector operation is
|
|
desired when both operands are strings. See L<perlop/"Bitwise String Operators">.
|
|
|
|
The following code will build up an ASCII string saying C<'PerlPerlPerl'>.
|
|
The comments show the string after each step. Note that this code works
|
|
in the same way on big-endian or little-endian machines.
|
|
|
|
my $foo = '';
|
|
vec($foo, 0, 32) = 0x5065726C; # 'Perl'
|
|
vec($foo, 2, 16) = 0x5065; # 'PerlPe'
|
|
vec($foo, 3, 16) = 0x726C; # 'PerlPerl'
|
|
vec($foo, 8, 8) = 0x50; # 'PerlPerlP'
|
|
vec($foo, 9, 8) = 0x65; # 'PerlPerlPe'
|
|
vec($foo, 20, 4) = 2; # 'PerlPerlPe' . "\x02"
|
|
vec($foo, 21, 4) = 7; # 'PerlPerlPer'
|
|
# 'r' is "\x72"
|
|
vec($foo, 45, 2) = 3; # 'PerlPerlPer' . "\x0c"
|
|
vec($foo, 93, 1) = 1; # 'PerlPerlPer' . "\x2c"
|
|
vec($foo, 94, 1) = 1; # 'PerlPerlPerl'
|
|
# 'l' is "\x6c"
|
|
|
|
To transform a bit vector into a string or array of 0's and 1's, use these:
|
|
|
|
$bits = unpack("b*", $vector);
|
|
@bits = split(//, unpack("b*", $vector));
|
|
|
|
If you know the exact length in bits, it can be used in place of the C<*>.
|
|
|
|
=item wait
|
|
|
|
Behaves like the wait(2) system call on your system: it waits for a child
|
|
process to terminate and returns the pid of the deceased process, or
|
|
C<-1> if there are no child processes. The status is rketurned in C<$?>.
|
|
Note that a return value of C<-1> could mean that child processes are
|
|
being automatically reaped, as described in L<perlipc>.
|
|
|
|
=item waitpid PID,FLAGS
|
|
|
|
Waits for a particular child process to terminate and returns the pid of
|
|
the deceased process, or C<-1> if there is no such child process. On some
|
|
systems, a value of 0 indicates that there are processes still running.
|
|
The status is returned in C<$?>. If you say
|
|
|
|
use POSIX ":sys_wait_h";
|
|
#...
|
|
do {
|
|
$kid = waitpid(-1,&WNOHANG);
|
|
} until $kid == -1;
|
|
|
|
then you can do a non-blocking wait for all pending zombie processes.
|
|
Non-blocking wait is available on machines supporting either the
|
|
waitpid(2) or wait4(2) system calls. However, waiting for a particular
|
|
pid with FLAGS of C<0> is implemented everywhere. (Perl emulates the
|
|
system call by remembering the status values of processes that have
|
|
exited but have not been harvested by the Perl script yet.)
|
|
|
|
Note that on some systems, a return value of C<-1> could mean that child
|
|
processes are being automatically reaped. See L<perlipc> for details,
|
|
and for other examples.
|
|
|
|
=item wantarray
|
|
|
|
Returns TRUE if the context of the currently executing subroutine is
|
|
looking for a list value. Returns FALSE if the context is looking
|
|
for a scalar. Returns the undefined value if the context is looking
|
|
for no value (void context).
|
|
|
|
return unless defined wantarray; # don't bother doing more
|
|
my @a = complex_calculation();
|
|
return wantarray ? @a : "@a";
|
|
|
|
=item warn LIST
|
|
|
|
Produces a message on STDERR just like C<die()>, but doesn't exit or throw
|
|
an exception.
|
|
|
|
If LIST is empty and C<$@> already contains a value (typically from a
|
|
previous eval) that value is used after appending C<"\t...caught">
|
|
to C<$@>. This is useful for staying almost, but not entirely similar to
|
|
C<die()>.
|
|
|
|
If C<$@> is empty then the string C<"Warning: Something's wrong"> is used.
|
|
|
|
No message is printed if there is a C<$SIG{__WARN__}> handler
|
|
installed. It is the handler's responsibility to deal with the message
|
|
as it sees fit (like, for instance, converting it into a C<die()>). Most
|
|
handlers must therefore make arrangements to actually display the
|
|
warnings that they are not prepared to deal with, by calling C<warn()>
|
|
again in the handler. Note that this is quite safe and will not
|
|
produce an endless loop, since C<__WARN__> hooks are not called from
|
|
inside one.
|
|
|
|
You will find this behavior is slightly different from that of
|
|
C<$SIG{__DIE__}> handlers (which don't suppress the error text, but can
|
|
instead call C<die()> again to change it).
|
|
|
|
Using a C<__WARN__> handler provides a powerful way to silence all
|
|
warnings (even the so-called mandatory ones). An example:
|
|
|
|
# wipe out *all* compile-time warnings
|
|
BEGIN { $SIG{'__WARN__'} = sub { warn $_[0] if $DOWARN } }
|
|
my $foo = 10;
|
|
my $foo = 20; # no warning about duplicate my $foo,
|
|
# but hey, you asked for it!
|
|
# no compile-time or run-time warnings before here
|
|
$DOWARN = 1;
|
|
|
|
# run-time warnings enabled after here
|
|
warn "\$foo is alive and $foo!"; # does show up
|
|
|
|
See L<perlvar> for details on setting C<%SIG> entries, and for more
|
|
examples. See the Carp module for other kinds of warnings using its
|
|
carp() and cluck() functions.
|
|
|
|
=item write FILEHANDLE
|
|
|
|
=item write EXPR
|
|
|
|
=item write
|
|
|
|
Writes a formatted record (possibly multi-line) to the specified FILEHANDLE,
|
|
using the format associated with that file. By default the format for
|
|
a file is the one having the same name as the filehandle, but the
|
|
format for the current output channel (see the C<select()> function) may be set
|
|
explicitly by assigning the name of the format to the C<$~> variable.
|
|
|
|
Top of form processing is handled automatically: if there is
|
|
insufficient room on the current page for the formatted record, the
|
|
page is advanced by writing a form feed, a special top-of-page format
|
|
is used to format the new page header, and then the record is written.
|
|
By default the top-of-page format is the name of the filehandle with
|
|
"_TOP" appended, but it may be dynamically set to the format of your
|
|
choice by assigning the name to the C<$^> variable while the filehandle is
|
|
selected. The number of lines remaining on the current page is in
|
|
variable C<$->, which can be set to C<0> to force a new page.
|
|
|
|
If FILEHANDLE is unspecified, output goes to the current default output
|
|
channel, which starts out as STDOUT but may be changed by the
|
|
C<select()> operator. If the FILEHANDLE is an EXPR, then the expression
|
|
is evaluated and the resulting string is used to look up the name of
|
|
the FILEHANDLE at run time. For more on formats, see L<perlform>.
|
|
|
|
Note that write is I<NOT> the opposite of C<read()>. Unfortunately.
|
|
|
|
=item y///
|
|
|
|
The transliteration operator. Same as C<tr///>. See L<perlop>.
|
|
|
|
=back
|