Here is the list of all the important functions supported by standard Perl.
abs - absolute value function
accept - accept an incoming socket connect
alarm - schedule a SIGALRM
atan2 - arctangent of Y/X in the range -PI to PI
bind - binds an address to a socket
binmode - prepare binary files for I/O
bless - create an object
caller - get context of the current subroutine call
chdir - change your current working directory
chmod - changes the permissions on a list of files
chomp - remove a trailing record separator from a string
chop - remove the last character from a string
chown - change the owership on a list of files
chr - get character this number represents
chroot - make directory new root for path lookups
close - close file (or pipe or socket) handle
closedir - close directory handle
connect - connect to a remote socket
continue - optional trailing block in a while or foreach
cos - cosine function
crypt - one-way passwd-style encryption
dbmclose - breaks binding on a tied dbm file
dbmopen - create binding on a tied dbm file
defined - test whether a value, variable, or function is defined or not
delete - deletes a value from a hash
die - raise an exception or bail out
do - turn a BLOCK into a TERM
dump - create an immediate core dump
each - retrieve the next key/value pair from a hash
endgrent - be done using group file
endhostent - be done using hosts file
endnetent - be done using networks file
endprotoent - be done using protocols file
endpwent - be done using passwd file
endservent - be done using services file
eof - test a filehandle for its end
eval - catch exceptions or compile and run code
exec - abandon this program to run another
exists - test whether a hash key is present
exit - terminate this program
exp - raise I to a power
fcntl - file control system call
fileno - return file descriptor from filehandle
flock - lock an entire file with an advisory lock
fork - create a new process just like this one
format - declare a picture format with use by the write() function
formline - internal function used for formats
getc - get the next character from the filehandle
getgrent - get next group record
getgrgid - get group record given group user ID
getgrnam - get group record given group name
gethostbyaddr - get host record given its address
gethostbyname - get host record given name
gethostent - get next hosts record
getlogin - return who logged in at this tty
getnetbyaddr - get network record given its address
getnetbyname - get networks record given name
getnetent - get next networks record
getpeername - find the other end of a socket connection
getpgrp - get process group
getppid - get parent process ID
getpriority - get current nice value
getprotobyname - get protocol record given name
getprotobynumber - get protocol record numeric protocol
getprotoent - get next protocols record
getpwent - get next passwd record
getpwnam - get passwd record given user login name
getpwuid - get passwd record given user ID
getservbyname - get services record given its name
getservbyport - get services record given numeric port
getservent - get next services record
getsockname - retrieve the sockaddr for a given socket
getsockopt - get socket options on a given socket
glob - expand filenames using wildcards
gmtime - convert UNIX time into record or string using Greenwich time format.
goto - create spaghetti code
grep - locate elements in a list test true against a given criterion
hex - convert a string to a hexadecimal number
import - patch a module's namespace into your own
index - find a substring within a string
int - get the integer portion of a number
ioctl - system-dependent device control system call
join - join a list into a string using a separator
keys - retrieve list of indices from a hash
kill - send a signal to a process or process group
last - exit a block prematurely
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
link - create a hard link in the filesytem
listen - register your socket as a server
local - create a temporary value for a global variable (dynamic scoping)
localtime - convert UNIX time into record or string using local time
lock - get a thread lock on a variable, subroutine, or method
log - retrieve the natural logarithm for a number
lstat - stat a symbolic link
m - match a string with a regular expression pattern
map - apply a change to a list to get back a new list with the changes
mkdir - create a directory
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
my - declare and assign a local variable (lexical scoping)
next - iterate a block prematurely
no - unimport some module symbols or semantics at compile time
oct - convert a string to an octal number
open - open a file, pipe, or descriptor
opendir - open a directory
ord - find a character's numeric representation
our - declare and assign a package variable (lexical scoping)
pack - convert a list into a binary representation
package - declare a separate global namespace
pipe - open a pair of connected filehandles
pop - remove the last element from an array and return it
pos - find or set the offset for the last/next m//g search
print - output a list to a filehandle
printf - output a formatted list to a filehandle
prototype - get the prototype (if any) of a subroutine
push - append one or more elements to an array
q - singly quote a string
qq - doubly quote a string
qr - Compile pattern
quotemeta - quote regular expression magic characters
qw - quote a list of words
qx - backquote quote a string
rand - retrieve the next pseudorandom number
read - fixed-length buffered input from a filehandle
readdir - get a directory from a directory handle
readline - fetch a record from a file
readlink - determine where a symbolic link is pointing
readpipe - execute a system command and collect standard output
recv - receive a message over a Socket
redo - start this loop iteration over again
ref - find out the type of thing being referenced
rename - change a filename
require - load in external functions from a library at runtime
reset - clear all variables of a given name
return - get out of a function early
reverse - flip a string or a list
rewinddir - reset directory handle
rindex - right-to-left substring search
rmdir - remove a directory
s - replace a pattern with a string
scalar - force a scalar context
seek - reposition file pointer for random-access I/O
seekdir - reposition directory pointer
select - reset default output or do I/O multiplexing
semctl - SysV semaphore control operations
semget - get set of SysV semaphores
semop - SysV semaphore operations
send - send a message over a socket
setgrent - prepare group file for use
sethostent - prepare hosts file for use
setnetent - prepare networks file for use
setpgrp - set the process group of a process
setpriority - set a process's nice value
setprotoent - prepare protocols file for use
setpwent - prepare passwd file for use
setservent - prepare services file for use
setsockopt - set some socket options
shift - remove the first element of an array, and return it
shmctl - SysV shared memory operations
shmget - get SysV shared memory segment identifier
shmread - read SysV shared memory
shmwrite - write SysV shared memory
shutdown - close down just half of a socket connection
sin - return the sine of a number
sleep - block for some number of seconds
socket - create a socket
socketpair - create a pair of sockets
sort - sort a list of values
splice - add or remove elements anywhere in an array
split - split up a string using a regexp delimiter
sprintf - formatted print into a string
sqrt - square root function
srand - seed the random number generator
stat - get a file's status information
study - optimize input data for repeated searches
sub - declare a subroutine, possibly anonymously
substr - get or alter a portion of a stirng
symlink - create a symbolic link to a file
syscall - execute an arbitrary system call
sysopen - open a file, pipe, or descriptor
sysread - fixed-length unbuffered input from a filehandle
sysseek - position I/O pointer on handle used with sysread and syswrite
system - run a separate program
syswrite - fixed-length unbuffered output to a filehandle
tell - get current seekpointer on a filehandle
telldir - get current seekpointer on a directory handle
tie - bind a variable to an object class
tied - get a reference to the object underlying a tied variable
time - return number of seconds since 1970
times - return elapsed time for self and child processes
tr - transliterate a string
truncate - shorten a file
uc - return upper-case version of a string
ucfirst - return a string with just the next letter in upper case
umask - set file creation mode mask
undef - remove a variable or function definition
unlink - remove one link to a file
unpack - convert binary structure into normal perl variables
unshift - prepend more elements to the beginning of a list
untie - break a tie binding to a variable
use - load in a module at compile time
utime - set a file's last access and modify times
values - return a list of the values in a hash
vec - test or set particular bits in a string
wait - wait for any child process to die
waitpid - wait for a particular child process to die
wantarray - get void vs scalar vs list context of current subroutine call
warn - print debugging info
write - print a picture record
-X - a file test (-r, -x, etc)
y - transliterate a string
