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Chapter 5. Function Reference

This chapter gives a brief description of Perl's built-in functions. Each description gives the syntax of the function, with the types and order of its arguments.

Required arguments are shown in italics, separated by commas. If an argument must be a specific variable type, that variable's identifier will be used (e.g., a percent sign for a hash, %hash). Optional arguments are placed in brackets. Do not use the brackets in function calls unless you really want to use an anonymous hash reference.

There are different ways to use a built-in function. For starters, any argument that requires a scalar value can be made up of any expression that returns one. For example, you can obtain the square root of the first value in an array:

$root = sqrt (shift @numbers);

shift removes the first element of @numbers and returns it to be used by sqrt.

Many functions take a list of scalars for arguments. Any array variable or other expression that returns a list can be used for all or part of the arguments. For example:

chmod (split /,/ FILELIST>); # An expression returns a list
chmod 0755, @executables;    # Array used for part of arguments

In the first line, the split expression reads a string from a filehandle and splits it into a list. The list provides proper arguments for chmod. The second line uses an array that contains a list of filenames for chmod to act upon.

Parentheses are not required around a function's arguments. However, without parentheses, functions are viewed as operators in an expression (the same is true of predeclared subroutines). If you use a function in a complex expression, you may want to use parentheses for clarity. See Chapter 4, "The Perl Language" for more about precedence in Perl expressions.

5.1. Perl Functions by Category

Here are Perl's functions and function-like keywords, arranged by category. Note that some functions appear in more than one category.

Scalar manipulation
chomp, chop, chr, crypt, hex, index, lc, lcfirst, length, oct, ord, pack, q//, qq//, reverse, rindex, sprintf, substr, tr///, uc, ucfirst, y///

Regular expressions and pattern matching
m//, pos, qr//, quotemeta, s///, split, study

Numeric functions
abs, atan2, cos, exp, hex, int, log, oct, rand, sin, sqrt, srand

Array processing
pop, push, shift, splice, unshift

List processing
grep, join, map, qw//, reverse, sort, unpack

Hash processing
delete, each, exists, keys, values

Input and output
binmode, close, closedir, dbmclose, dbmopen, die, eof, fileno, flock, format, getc, print, printf, read, readdir, rewinddir, seek, seekdir, select, syscall, sysread, sysseek, syswrite, tell, telldir, truncate, warn, write

Fixed-length data and records
pack, read, syscall, sysread, syswrite, unpack, vec

Filehandles, files, and directories
chdir, chmod, chown, chroot, fcntl, glob, ioctl, link, lstat, mkdir, open, opendir, readlink, rename, rmdir, stat, symlink, sysopen, umask, unlink, utime

Flow of program control
caller, continue, die, do, dump, eval, exit, goto, last, next, redo, return, sub, wantarray

caller, import, local, my, package, use

defined, dump, eval, formline, local, my, prototype, reset, scalar, undef, wantarray

Processes and process groups
alarm, exec, fork, getpgrp, getppid, getpriority, kill, pipe, qx//, setpgrp, setpriority, sleep, system, times, wait, waitpid

Library modules
do, import, no, package, require, use

Classes and objects
bless, dbmclose, dbmopen, package, ref, tie, tied, untie, use

Low-level socket access
accept, bind, connect, getpeername, getsockname, getsockopt, listen, recv, send, setsockopt, shutdown, socket, socketpair

System V interprocess communication
msgctl, msgget, msgrcv, msgsnd, semctl, semget, semop, shmctl, shmget, shmread, shmwrite

Fetching user and group information
endgrent, endhostent, endnetent, endpwent, getgrent, getgrgid, getgrnam, get-login, getpwent, getpwnam, getpwuid, setgrent, setpwent

Fetching network information
endprotoent, endservent, gethostbyaddr, gethostbyname, gethostent, getnet-byaddr, getnetbyname, getnetent, getprotobyname, getprotobynumber, getprotoent, getservbyname, getservbyport, getservent, sethostent, setnet-ent, setprotoent, setservent

gmtime, localtime, time, times

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