• Functions for SCALARs or strings
• Regular expressions and pattern matching
• Numeric functions
• Functions for real @ARRAYs
• Functions for list data
• Functions for real %HASHes
• Input and output functions
• Functions for fixed length data or records
• Functions for filehandles, files, or directories
• Keywords related to control flow of your perl program
• Keywords altering or affecting scoping of identifiers
• Miscellaneous functions
• Functions for processes and process groups
• Keywords related to perl modules
• Keywords related to classes and object-orientedness
• Low-level socket functions
• System V interprocess communication functions
• Fetching user and group info
• Fetching network info
• Time-related functions

Functions for SCALARs or strings

• chomp - remove a trailing record separator from a string
• chop - remove the last character from a string
• chr - get character this number represents
• crypt - one-way passwd-style encryption
• hex - convert a string to a hexadecimal number
• index - find a substring within a string
• lc - return lower-case version of a string
• lcfirst - return a string with just the next letter in lower case
• length - return the number of bytes in a string
• oct - convert a string to an octal number
• ord - find a character's numeric representation
• pack - convert a list into a binary representation
• q/STRING/ - singly quote a string
• qq/STRING/ - doubly quote a string
• reverse - flip a string or a list
• rindex - right-to-left substring search
• sprintf - formatted print into a string
• substr - get or alter a portion of a stirng
• tr/// - transliterate a string
• uc - return upper-case version of a string
• ucfirst - return a string with just the next letter in upper case
• y/// - transliterate a string

Regular expressions and pattern matching

• m// - match a string with a regular expression pattern
• pos - find or set the offset for the last/next m//g search
• qr/STRING/ - Compile pattern
• quotemeta - quote regular expression magic characters
• s/// - replace a pattern with a string
• split - split up a string using a regexp delimiter
• study - optimize input data for repeated searches

Numeric functions

• abs - absolute value function
• atan2 - arctangent of Y/X in the range -PI to PI
• cos - cosine function
• exp - raise I to a power
• hex - convert a string to a hexadecimal number
• int - get the integer portion of a number
• log - retrieve the natural logarithm for a number
• oct - convert a string to an octal number
• rand - retrieve the next pseudorandom number
• sin - return the sine of a number
• sqrt - square root function
• srand - seed the random number generator

Functions for real @ARRAYs

• pop - remove the last element from an array and return it
• push - append one or more elements to an array
• shift - remove the first element of an array, and return it
• splice - add or remove elements anywhere in an array
• unshift - prepend more elements to the beginning of a list

Functions for list data

• grep - locate elements in a list test true against a given criterion
• join - join a list into a string using a separator
• map - apply a change to a list to get back a new list with the changes
• qw/STRING/ - quote a list of words
• reverse - flip a string or a list
• sort - sort a list of values
• unpack - convert binary structure into normal perl variables

Functions for real %HASHes

• delete - deletes a value from a hash
• each - retrieve the next key/value pair from a hash
• exists - test whether a hash key is present
• keys - retrieve list of indices from a hash
• values - return a list of the values in a hash

Input and output functions

• binmode - prepare binary files for I/O
• close - close file (or pipe or socket) handle
• closedir - close directory handle
• dbmclose - breaks binding on a tied dbm file
• dbmopen - create binding on a tied dbm file
• die - raise an exception or bail out
• eof - test a filehandle for its end
• fileno - return file descriptor from filehandle
• flock - lock an entire file with an advisory lock
• format - declare a picture format with use by the write() function
• getc - get the next character from the filehandle
• print - output a list to a filehandle
• printf - output a formatted list to a filehandle
• read - fixed-length buffered input from a filehandle
• readdir - get a directory from a directory handle
• readline - fetch a record from a file
• rewinddir - reset directory handle
• seek - reposition file pointer for random-access I/O
• seekdir - reposition directory pointer
• select - reset default output or do I/O multiplexing
• syscall - execute an arbitrary system call
• sysread - fixed-length unbuffered input from a filehandle
• sysseek - position I/O pointer on handle used with sysread and syswrite
• syswrite - fixed-length unbuffered output to a filehandle
• tell - get current seekpointer on a filehandle
• telldir - get current seekpointer on a directory handle
• truncate - shorten a file
• warn - print debugging info
• write - print a picture record

Functions for fixed length data or records

• pack - convert a list into a binary representation
• read - fixed-length buffered input from a filehandle
• syscall - execute an arbitrary system call
• sysread - fixed-length unbuffered input from a filehandle
• sysseek - position I/O pointer on handle used with sysread and syswrite
• syswrite - fixed-length unbuffered output to a filehandle
• unpack - convert binary structure into normal perl variables
• vec - test or set particular bits in a string

Functions for filehandles, files, or directories

• -X - a file test (-r, -x, etc)
• chdir - change your current working directory
• chmod - changes the permissions on a list of files
• chown - change the owership on a list of files
• chroot - make directory new root for path lookups
• fcntl - file control system call
• glob - expand filenames using wildcards
• ioctl - system-dependent device control system call
• link - create a hard link in the filesytem
• lstat - stat a symbolic link
• mkdir - create a directory
• open - open a file, pipe, or descriptor
• opendir - open a directory
• readlink - determine where a symbolic link is pointing
• rename - change a filename
• rmdir - remove a directory
• stat - get a file's status information
• symlink - create a symbolic link to a file
• sysopen - open a file, pipe, or descriptor
• umask - set file creation mode mask
• unlink - remove one link to a file
• utime - set a file's last access and modify times

Keywords related to control flow of your perl program

• caller - get context of the current subroutine call
• continue - optional trailing block in a while or foreach
• die - raise an exception or bail out
• do - turn a BLOCK into a TERM
• dump - create an immediate core dump
• eval - catch exceptions or compile and run code
• exit - terminate this program
• goto - create spaghetti code
• last - exit a block prematurely
• next - iterate a block prematurely
• prototype - get the prototype (if any) of a subroutine
• redo - start this loop iteration over again
• return - get out of a function early
• sub - declare a subroutine, possibly anonymously
• wantarray - get void vs scalar vs list context of current subroutine call

Keywords altering or affecting scoping of identifiers

• caller - get context of the current subroutine call
• import - patch a module's namespace into your own
• local - create a temporary value for a global variable (dynamic scoping)
• my - declare and assign a local variable (lexical scoping)
• our - declare and assign a package variable (lexical scoping)
• package - declare a separate global namespace
• use - load in a module at compile time

Miscellaneous functions

• defined - test whether a value, variable, or function is defined
• dump - create an immediate core dump
• eval - catch exceptions or compile and run code
• formline - internal function used for formats
• local - create a temporary value for a global variable (dynamic scoping)
• my - declare and assign a local variable (lexical scoping)
• our - declare and assign a package variable (lexical scoping)
• prototype - get the prototype (if any) of a subroutine
• reset - clear all variables of a given name
• scalar - force a scalar context
• undef - remove a variable or function definition
• wantarray - get void vs scalar vs list context of current subroutine call

Functions for processes and process groups

• alarm - schedule a SIGALRM
• exec - abandon this program to run another
• fork - create a new process just like this one
• getpgrp - get process group
• getppid - get parent process ID
• getpriority - get current nice value
• kill - send a signal to a process or process group
• pipe - open a pair of connected filehandles
• qx/STRING/ - backquote quote a string
• readpipe - execute a system command and collect standard output
• setpgrp - set the process group of a process
• setpriority - set a process's nice value
• sleep - block for some number of seconds
• system - run a separate program
• times - return elapsed time for self and child processes
• wait - wait for any child process to die
• waitpid - wait for a particular child process to die

Keywords related to perl modules

• do - turn a BLOCK into a TERM
• import - patch a module's namespace into your own
• no - unimport some module symbols or semantics at compile time
• package - declare a separate global namespace
• require - load in external functions from a library at runtime
• use - load in a module at compile time

Keywords related to classes and object-orientedness

• bless - create an object
• dbmclose - breaks binding on a tied dbm file
• dbmopen - create binding on a tied dbm file
• package - declare a separate global namespace
• ref - find out the type of thing being referenced
• tie - bind a variable to an object class
• tied - get a reference to the object underlying a tied variable
• untie - break a tie binding to a variable
• use - load in a module at compile time

Low-level socket functions

• accept - accept an incoming socket connect
• bind - binds an address to a socket
• connect - connect to a remote socket
• getpeername - find the other end of a socket connection
• getsockname - retrieve the sockaddr for a given socket
• getsockopt - get socket options on a given socket
• listen - register your socket as a server
• recv - receive a message over a Socket
• send - send a message over a socket
• setsockopt - set some socket options
• shutdown - close down just half of a socket connection
• socket - create a socket
• socketpair - create a pair of sockets

System V interprocess communication functions

• msgctl - SysV IPC message control operations
• msgget - get SysV IPC message queue
• msgrcv - receive a SysV IPC message from a message queue
• msgsnd - send a SysV IPC message to a message queue
• semctl - SysV semaphore control operations
• semget - get set of SysV semaphores
• semop - SysV semaphore operations
• shmctl - SysV shared memory operations
• shmget - get SysV shared memory segment identifier
• shmread - read SysV shared memory
• shmwrite - write SysV shared memory

Fetching user and group info

• endgrent - be done using group file
• endhostent - be done using hosts file
• endnetent - be done using networks file
• endpwent - be done using passwd file
• getgrent - get next group record
• getgrgid - get group record given group user ID
• getgrnam - get group record given group name
• getlogin - return who logged in at this tty
• getpwent - get next passwd record
• getpwnam - get passwd record given user login name
• getpwuid - get passwd record given user ID
• setgrent - prepare group file for use
• setpwent - prepare passwd file for use

Fetching network info

• endprotoent - be done using protocols file
• endservent - be done using services file
• gethostbyaddr - get host record given its address
• gethostbyname - get host record given name
• gethostent - get next hosts record
• getnetbyaddr - get network record given its address
• getnetbyname - get networks record given name
• getnetent - get next networks record
• getprotobyname - get protocol record given name
• getprotobynumber - get protocol record numeric protocol
• getprotoent - get next protocols record
• getservbyname - get services record given its name
• getservbyport - get services record given numeric port
• getservent - get next services record
• sethostent - prepare hosts file for use
• setnetent - prepare networks file for use
• setprotoent - prepare protocols file for use
• setservent - prepare services file for use

Time-related functions

• gmtime - convert UNIX time into record or string using Greenwich time
• localtime - convert UNIX time into record or string using local time
• time - return number of seconds since 1970
• times - return elapsed time for self and child processes