perlfunc - Perl builtin functions
The functions in this section can serve as terms in an expression. They fall into two major categories: list operators and named unary operators. These differ in their precedence relationship with a following comma. (See the precedence table in perlop.) List operators take more than one argument, while unary operators can never take more than one argument. Thus, a comma terminates the argument of a unary operator, but merely separates the arguments of a list operator. A unary operator generally provides scalar context to its argument, while a list operator may provide either scalar or list contexts for its arguments. If it does both, scalar arguments come first and list argument follow, and there can only ever be one such list argument. For instance, splice() has three scalar arguments followed by a list, whereas gethostbyname() has four scalar arguments.
In the syntax descriptions that follow, list operators that expect a list (and provide list context for elements of the list) are shown with LIST as an argument. Such a list may consist of any combination of scalar arguments or list values; the list values will be included in the list as if each individual element were interpolated at that point in the list, forming a longer single-dimensional list value. Commas should separate literal elements of the LIST.
Any function in the list below may be used either with or without parentheses around its arguments. (The syntax descriptions omit the parentheses.) If you use parentheses, the simple but occasionally surprising rule is this: It looks like a function, therefore it is a function, and precedence doesn't matter. Otherwise it's a list operator or unary operator, and precedence does matter. Whitespace between the function and left parenthesis doesn't count, so sometimes you need to be careful:
print 1+2+4; # Prints 7.
print(1+2) + 4; # Prints 3.
print (1+2)+4; # Also prints 3!
print +(1+2)+4; # Prints 7.
print ((1+2)+4); # Prints 7.If you run Perl with the -w switch it can warn you about this. For example, the third line above produces:
print (...) interpreted as function at - line 1.
Useless use of integer addition in void context at - line 1.A few functions take no arguments at all, and therefore work as neither unary nor list operators. These include such functions as time and endpwent. For example, time+86_400 always means time() + 86_400.
For functions that can be used in either a scalar or list context, nonabortive failure is generally indicated in scalar context by returning the undefined value, and in list context by returning the empty list.
Remember the following important rule: There is no rule that relates the behavior of an expression in list context to its behavior in scalar context, or vice versa. It might do two totally different things. Each operator and function decides which sort of value would be most appropriate to return in scalar context. Some operators return the length of the list that would have been returned in list context. Some operators return the first value in the list. Some operators return the last value in the list. Some operators return a count of successful operations. In general, they do what you want, unless you want consistency.
A named array in scalar context is quite different from what would at first glance appear to be a list in scalar context. You can't get a list like (1,2,3) into being in scalar context, because the compiler knows the context at compile time. It would generate the scalar comma operator there, not the list construction version of the comma. That means it was never a list to start with.
In general, functions in Perl that serve as wrappers for system calls ("syscalls") of the same name (like chown(2), fork(2), closedir(2), etc.) return true when they succeed and undef otherwise, as is usually mentioned in the descriptions below. This is different from the C interfaces, which return -1 on failure. Exceptions to this rule include wait, waitpid, and syscall. System calls also set the special $! variable on failure. Other functions do not, except accidentally.
Extension modules can also hook into the Perl parser to define new kinds of keyword-headed expression. These may look like functions, but may also look completely different. The syntax following the keyword is defined entirely by the extension. If you are an implementor, see "PL_keyword_plugin" in perlapi for the mechanism. If you are using such a module, see the module's documentation for details of the syntax that it defines.
Here are Perl's functions (including things that look like functions, like some keywords and named operators) arranged by category. Some functions appear in more than one place.
chomp, chop, chr, crypt, fc, hex, index, lc, lcfirst, length, oct, ord, pack, q//, qq//, reverse, rindex, sprintf, substr, tr///, uc, ucfirst, y///
fc is available only if the "fc" feature is enabled or if it is prefixed with CORE::. The "fc" feature is enabled automatically with a use v5.16 (or higher) declaration in the current scope.
m//, pos, qr//, quotemeta, s///, split, study
abs, atan2, cos, exp, hex, int, log, oct, rand, sin, sqrt, srand
each, keys, pop, push, shift, splice, unshift, values
grep, join, map, qw//, reverse, sort, unpack
delete, each, exists, keys, values
binmode, close, closedir, dbmclose, dbmopen, die, eof, fileno, flock, format, getc, print, printf, read, readdir, readline rewinddir, say, seek, seekdir, select, syscall, sysread, sysseek, syswrite, tell, telldir, truncate, warn, write
say is available only if the "say" feature is enabled or if it is prefixed with CORE::. The "say" feature is enabled automatically with a use v5.10 (or higher) declaration in the current scope.
pack, read, syscall, sysread, sysseek, syswrite, unpack, vec
-X, chdir, chmod, chown, chroot, fcntl, glob, ioctl, link, lstat, mkdir, open, opendir, readlink, rename, rmdir, stat, symlink, sysopen, umask, unlink, utime
break, caller, continue, die, do, dump, eval, evalbytes exit, __FILE__, goto, last, __LINE__, next, __PACKAGE__, redo, return, sub, __SUB__, wantarray
break is available only if you enable the experimental "switch" feature or use the CORE:: prefix. The "switch" feature also enables the default, given and when statements, which are documented in "Switch Statements" in perlsyn. The "switch" feature is enabled automatically with a use v5.10 (or higher) declaration in the current scope. In Perl v5.14 and earlier, continue required the "switch" feature, like the other keywords.
evalbytes is only available with the "evalbytes" feature (see feature) or if prefixed with CORE::. __SUB__ is only available with the "current_sub" feature or if prefixed with CORE::. Both the "evalbytes" and "current_sub" features are enabled automatically with a use v5.16 (or higher) declaration in the current scope.
caller, import, local, my, our, package, state, use
state is available only if the "state" feature is enabled or if it is prefixed with CORE::. The "state" feature is enabled automatically with a use v5.10 (or higher) declaration in the current scope.
defined, formline, lock, prototype, reset, scalar, undef
alarm, exec, fork, getpgrp, getppid, getpriority, kill, pipe, qx//, readpipe, setpgrp, setpriority, sleep, system, times, wait, waitpid
do, import, no, package, require, use
bless, dbmclose, dbmopen, package, ref, tie, tied, untie, use
accept, bind, connect, getpeername, getsockname, getsockopt, listen, recv, send, setsockopt, shutdown, socket, socketpair
msgctl, msgget, msgrcv, msgsnd, semctl, semget, semop, shmctl, shmget, shmread, shmwrite
endgrent, endhostent, endnetent, endpwent, getgrent, getgrgid, getgrnam, getlogin, getpwent, getpwnam, getpwuid, setgrent, setpwent
endprotoent, endservent, gethostbyaddr, gethostbyname, gethostent, getnetbyaddr, getnetbyname, getnetent, getprotobyname, getprotobynumber, getprotoent, getservbyname, getservbyport, getservent, sethostent, setnetent, setprotoent, setservent
gmtime, localtime, time, times
and, AUTOLOAD, BEGIN, CHECK, cmp, CORE, __DATA__, default, DESTROY, else, elseif, elsif, END, __END__, eq, for, foreach, ge, given, gt, if, INIT, le, lt, ne, not, or, UNITCHECK, unless, until, when, while, x, xor
Perl was born in Unix and can therefore access all common Unix system calls. In non-Unix environments, the functionality of some Unix system calls may not be available or details of the available functionality may differ slightly. The Perl functions affected by this are:
-X, binmode, chmod, chown, chroot, crypt, dbmclose, dbmopen, dump, endgrent, endhostent, endnetent, endprotoent, endpwent, endservent, exec, fcntl, flock, fork, getgrent, getgrgid, gethostbyname, gethostent, getlogin, getnetbyaddr, getnetbyname, getnetent, getppid, getpgrp, getpriority, getprotobynumber, getprotoent, getpwent, getpwnam, getpwuid, getservbyport, getservent, getsockopt, glob, ioctl, kill, link, lstat, msgctl, msgget, msgrcv, msgsnd, open, pipe, readlink, rename, select, semctl, semget, semop, setgrent, sethostent, setnetent, setpgrp, setpriority, setprotoent, setpwent, setservent, setsockopt, shmctl, shmget, shmread, shmwrite, socket, socketpair, stat, symlink, syscall, sysopen, system, times, truncate, umask, unlink, utime, wait, waitpid
For more information about the portability of these functions, see perlport and other available platform-specific documentation.
A file test, where X is one of the letters listed below. This unary operator takes one argument, either a filename, a filehandle, or a dirhandle, and tests the associated file to see if something is true about it. If the argument is omitted, tests $_, except for -t, which tests STDIN. Unless otherwise documented, it returns 1 for true and '' for false. If the file doesn't exist or can't be examined, it returns undef and sets $! (errno). Despite the funny names, precedence is the same as any other named unary operator. The operator may be any of:
-r File is readable by effective uid/gid.
-w File is writable by effective uid/gid.
-x File is executable by effective uid/gid.
-o File is owned by effective uid.
-R File is readable by real uid/gid.
-W File is writable by real uid/gid.
-X File is executable by real uid/gid.
-O File is owned by real uid.
-e File exists.
-z File has zero size (is empty).
-s File has nonzero size (returns size in bytes).
-f File is a plain file.
-d File is a directory.
-l File is a symbolic link.
-p File is a named pipe (FIFO), or Filehandle is a pipe.
-S File is a socket.
-b File is a block special file.
-c File is a character special file.
-t Filehandle is opened to a tty.
-u File has setuid bit set.
-g File has setgid bit set.
-k File has sticky bit set.
-T File is an ASCII text file (heuristic guess).
-B File is a "binary" file (opposite of -T).
-M Script start time minus file modification time, in days.
-A Same for access time.
-C Same for inode change time (Unix, may differ for other
platforms)Example:
while (<>) {
chomp;
next unless -f $_; # ignore specials
#...
}Note that -s/a/b/ does not do a negated substitution. Saying -exp($foo) still works as expected, however: only single letters following a minus are interpreted as file tests.
These operators are exempt from the "looks like a function rule" described above. That is, an opening parenthesis after the operator does not affect how much of the following code constitutes the argument. Put the opening parentheses before the operator to separate it from code that follows (this applies only to operators with higher precedence than unary operators, of course):
-s($file) + 1024 # probably wrong; same as -s($file + 1024)
(-s $file) + 1024 # correctThe interpretation of the file permission operators -r, -R, -w, -W, -x, and -X is by default based solely on the mode of the file and the uids and gids of the user. There may be other reasons you can't actually read, write, or execute the file: for example network filesystem access controls, ACLs (access control lists), read-only filesystems, and unrecognized executable formats. Note that the use of these six specific operators to verify if some operation is possible is usually a mistake, because it may be open to race conditions.
Also note that, for the superuser on the local filesystems, the -r, -R, -w, and -W tests always return 1, and -x and -X return 1 if any execute bit is set in the mode. Scripts run by the superuser may thus need to do a stat() to determine the actual mode of the file, or temporarily set their effective uid to something else.
If you are using ACLs, there is a pragma called filetest that may produce more accurate results than the bare stat() mode bits. When under use filetest 'access' the above-mentioned filetests test whether the permission can(not) be granted using the access(2) family of system calls. Also note that the -x and -X may under this pragma return true even if there are no execute permission bits set (nor any extra execute permission ACLs). This strangeness is due to the underlying system calls' definitions. Note also that, due to the implementation of use filetest 'access', the _ special filehandle won't cache the results of the file tests when this pragma is in effect. Read the documentation for the filetest pragma for more information.
The -T and -B switches work as follows. The first block or so of the file is examined for odd characters such as strange control codes or characters with the high bit set. If too many strange characters (>30%) are found, it's a -B file; otherwise it's a -T file. Also, any file containing a zero byte in the first block is considered a binary file. If -T or -B is used on a filehandle, the current IO buffer is examined rather than the first block. Both -T and -B return true on an empty file, or a file at EOF when testing a filehandle. Because you have to read a file to do the -T test, on most occasions you want to use a -f against the file first, as in next unless -f $file && -T $file.
If any of the file tests (or either the stat or lstat operator) is given the special filehandle consisting of a solitary underline, then the stat structure of the previous file test (or stat operator) is used, saving a system call. (This doesn't work with -t, and you need to remember that lstat() and -l leave values in the stat structure for the symbolic link, not the real file.) (Also, if the stat buffer was filled by an lstat call, -T and -B will reset it with the results of stat _). Example:
print "Can do.\n" if -r $a || -w _ || -x _;
stat($filename);
print "Readable\n" if -r _;
print "Writable\n" if -w _;
print "Executable\n" if -x _;
print "Setuid\n" if -u _;
print "Setgid\n" if -g _;
print "Sticky\n" if -k _;
print "Text\n" if -T _;
print "Binary\n" if -B _;As of Perl 5.10.0, as a form of purely syntactic sugar, you can stack file test operators, in a way that -f -w -x $file is equivalent to -x $file && -w _ && -f _. (This is only fancy syntax: if you use the return value of -f $file as an argument to another filetest operator, no special magic will happen.)
Portability issues: "-X" in perlport.
To avoid confusing would-be users of your code with mysterious syntax errors, put something like this at the top of your script:
use 5.010; # so filetest ops can stackReturns the absolute value of its argument. If VALUE is omitted, uses $_.
Accepts an incoming socket connect, just as accept(2) does. Returns the packed address if it succeeded, false otherwise. See the example in "Sockets: Client/Server Communication" in perlipc.
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 $^F. See "$^F" in perlvar.