Perl network programming cheat sheet

perldoc perldoc

Look up Perl documentation in Pod format

perldoc perltoc

Perl documentation Table of Contents (ToC)

perldoc perl

Basics language interpreter

perldoc perlfunc

List of built-in Perl functions

perldoc -f

Help with a specific function

perldoc perlop

List of Perl operators and precedence

perldoc perlmodlib

For constructing perl modules and finding existing ones

perldoc perllocal

Locally installed modules list (if any)

perldoc

Documentation for specific module

Less than

<

lt

Greater than

>

gt

Less than or equal

<=

le

Greater than or equal

>=

ge

Equality

==

eq

Inequality

!=

ne

Description

Example

C-style Logical AND operator

&&

($a && $b) is false

Logical AND operator

and

($a and $b) is false

C-style Logical OR operator

||

($a || $b) is true

Logical OR operator

or

($a or $b) is true

C-style Logical NOT operator

!

!($a) is false

Logical NOT operator

not

not($a) is false

Single-quotes - Literal data enclosing

$bar = 'it is worth $foo';

it is worth $foo

Double-quotes - Interpolated data enclosing

$bar = "it is worth $foo";

it is worth 5

Escape characters

$bar = "it is \"worth\" $foo";

$bar = 'it is \'worth\' $foo';

it is "worth" 5
it is 'worth' $foo

Without quotes

$bar = q(it is 'worth' $foo);

$bar = qq(it is "worth" $foo);

it is 'worth' $foo
it is "worth" 5

left

terms and list operators

See below.

left

->

Infix dereference operator

=++

Auto-increment (magical on strings).

--

Auto-decrement.

right

**

Exponentiation.

right

\

Reference to an object (unary).

right

! ~

Unary negation, bitwise complement.

right

+ -

Unary plus, minus.

left

= ~

Binds a scalar expression to a pattern match.

left

! ~

Same, but negates the result.

left

* / % x

Multiplication, division, modulo, repetition.

left

+ - .

Addition, subtraction, concatenation

left

>> <<

Bitwise shift right, bitwise shift left.

named unary operators

E.g. sin, chdir, -f, -M.

< > <= >=

lt gt le ge

Numerical relational operators.

String relational operators.

== != <=>

eq ne cmp

Numerical equal, not equal, compare.

Stringwise equal, not equal, compare.

Compare operators return -1 (less), 0 (equal)

or 1 (greater).

left

&

Bitwise AND.

left

| ˆ

Bitwise OR, exclusive OR.

left

&&

Logical AND.

left

||

Logical OR.

..

In scalar context, range operator.

In array context, enumeration.

right

? :

Conditional (if ? then : else) operator.

right

= += -= *= etc.

Assignment operators.

left

,

Comma operator, also list element separator.

left

=>

Same, enforces the left operand to be a string.

list operators (rightward)

See below.

right

not

Low precedence logical NOT.

left

and

Low precedence logical AND.

left

or xor

Low precedence logical OR, exclusive OR.

-0[octal/hexadecimal]

Specifies the input record separator ($/ ) as an octal or hexadecimal number

-a

Turns on autosplit mode when used with a -n or -p

-c

Causes Perl to check the syntax of the program and then exit without executing it

-C [number/list]

The -C flag controls some of the Perl Unicode features.

-d, -dt

Runs the program under the Perl debugger

-Dletters, -Dnumber

Sets debugging flags (only if your perl binary has been built with debugging enabled)

-e commandline

May be used to enter one line of program

-E commandline

Like -e, except it implicitly enables all optional features (in the main compilation unit)

-f

Disable executing $Config{sitelib}/sitecustomize.pl at startup

-F pattern

Specifies the pattern to split on for -a (regex // , "" , or '')

-h

Prints summary if the options

-m

-mmodule executes use module (); before executing your program

-M

-Mmodule executes use module ; before executing your program

-n

Input loop in the script without line printing

-p

Input loop in the script with line printing

-S

Makes Perl use the PATH environment variable to search for the program

-T

Turns on taint so you can test

-v

Prints the version and patchlevel of your perl executable

-V

Prints summary of the major perl configuration values and the current values of @INC

-w

Prints warnings about dubious constructs

-xdirectory

Tells Perl that the program is embedded in a larger chunk of unrelated text

$

Default variable

$/

The input record separator, newline by default

$\

The output record separator for the print operator

$(

The real GID (Group ID) of this process

$)

The effective GID (Group ID) of this process

$&

The string matched by the last successful pattern match

$`

The string preceding whatever was matched by the last successful pattern match

$'

The string following whatever was matched by the last successful pattern match

$ARGV

Contains the name of the current file when reading from <>

@ARGV

The array @ARGV contains the command-line arguments intended for the script

%ENV

The hash %ENV contains your current environment

@_

Within a subroutine the array @_ contains the parameters passed to that subroutine

@INC

Contains the list of places that the do EXPR , require, or use constructs look for their library files

$~

The name of the current report format for the currently selected output channel

$^

The name of the current top-of-page format for the currently selected output channel

$^A

The current value of the write() accumulator for format() lines

$^L

What formats output as a form feed. The default is \f

$^T

The time at which the program began running, in seconds since the epoch (beginning of 1970)

$^X

The name used to execute the current copy of Perl

$!

Each element of %! has a true value only if $! is set to that value - %ERRNO

$@

The Perl error from the last eval operator, i.e. the last exception that was caught

$?

The status returned by the last pipe close, backtick (`` ) command, successful call to wait() or waitpid(), or from the system() operator

$.

Current line number for the last filehandle accessed.

$%

The current page number of the currently selected output channel

$=

The current page length (printable lines) of the currently selected output channel. The default is 60

$-

The number of lines left on the page of the currently selected output channel

$|

If set to nonzero, forces a flush right away and after every write or print on the currently selected output channel

$0

Contains the name of the program being executed

$+

The text matched by the highest used capture group of the last successful search pattern

-e

Single line of script

-w

Warnings

-c

Checks syntax

-n

Input loop without printing

-p

Printing an input loop

-a

Automatic split

-M

Load a module

-U

Unsafe operations mode

-v

Version and patch level of script

\

reference

[ ]

arrayref

{ }

hashref

\( )

List of refs

$var

Default variable

$var[20]

21st element of array @var

$p = \@var

Now $p is a reference to @var

$$p[20]

21st element of array referenced by $p

$var[-1]

Last element of array @var

$var[$x][$y]

$y-th element of $x-th element of array @var

$var{’JAN’}

A value from ‘hash’ %var

$p = \%var

Now $p is a reference to hash %var

$$p{’JAN’}

A value from hash referenced by $p

$#var

Last index of array @var

@var

The entire array

@var[5,6,7]

A slice of array @var

@var{’X’,’Y’}

A slice of %var; same as ($var{’X’},$var{’Y’})

%var

The entire hash;

$var{’a’,1,...}

Emulates a multidimensional array;

@arr = (1..3);

Array initialization

$i = @arr;

Number of elements in the array

@arr = split(­/-/­,$text);

Split the string into $text

push(@arr, $s);

Append $s to @arr

$arr = pop(@arr);

Removes the last element in the array

chop(@arr);

Removes the last character in the array

Special variables

@ARGV array which stores all the command line arguments

@ENV hash of program’s environment

abs

Absolute value

accept

Accept an incoming socket connection

bind

Binds an address to a socket

binmode

Prepare binary files for input/output

chdir

Change current working directory

chmod

Changes the permissions on a file/list of files

chop

Remove the last character from a string

chown

Change the ownership of the file

close

Close file

closedir

Close directory

connect

Connect to a remote socket

crypt

One-way encryption

delete

Deletes a value from a hash

die

Raise an exception

dump

Create a core dump immediately

eof

End of file

eval

Compile and run code

exit

Terminate running s program

exp

Exponential

fork

Create a new process just like the existing one

gethostbyaddr

Get host record IP address

gethostbyname

Get host record given name

getlogin

Return who is logged in at this TTY

getnetbyname

Get networks record given name

getnetent

Get next networks record

getpeername

FInd the other end of a socket connection

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

hex

Convert a string to a hexadecimal number

join

Join a list into a string using a separator

kill

Send a signal to a process or process group

length

Return the number of bytes in a string

listen

Register your socket as a server

m

Match a string with a regular expression pattern

mkdir

Create a directory

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)

package

Declare a separate global namespace

print

Output a list to a filehandle

printf

Output redirect to a filehandle

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

readpipe

Run a system command and collect standard output

recv

Receive a message via a Socket

rename

Change a filename

return

Exit function early

rmdir

Remove a directory

send

Send a message via a socket

shift

Remove the first element of an array

shutdown

Terminate half of the socket connection

socket

Create a socket

sort

Sort a list of values

sqrt

Square root function

syscall

Execute an arbitrary system call