perl network programming

All the tables provided in the cheat sheets are also presented in tables below which are easy to copy and paste.

The Perl Network Programming Cheat Sheet covers:

  • Perl help
  • Comparison operators
  • Command-line arguments
  • Special variables
  • Run mode options
  • References
  • Variables
  • Arrays
  • Socket programming with Server-side & Client-side examples
  • Relevant Perl functions

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Network Programming with Perl Cheat Sheet

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What’s included in this cheat sheet

The following categories and items have been included in the cheat sheet:

Perl help

Install Package


$ sudo apt-get install perl-doc

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


Comparison operators

Arithmetic


Strings


 

Less than


<

lt

Greater than


>

gt

Less than or equal


<=

le

Greater than or equal


>=

ge

Equality


==

eq

Inequality


!=

ne

Boolean operators


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


Quotes ($foo = 5;)


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


Assoc


Operators


Description


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.


Command-line Arguments

-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


Special Variables

$


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


Run mode options

-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


References

\


reference


[ ]


arrayref


{ }


hashref


\( )


List of refs


Variables

$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;


Arrays

@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


Socket Programming with Server-side & Client-side examples

Server-side Method


socket() call- socket( SOCKET, DOMAIN, TYPE, PROTOCOL );
bind() call -bind( SOCKET, ADDRESS );
listen() call- listen( SOCKET, QUEUESIZE );
accept() call - accept( NEW_SOCKET, SOCKET );

Server-side Socket Script Example


#!/usr/bin/perl -w
# Filename : serversocket.pl

use strict;
use Socket;

# use port 7999
my $port = shift || 7999;
my $proto = getprotobyname('tcp');
my $server = "localhost"; # Host IP running the server

# create a socket
socket(SOCKET, PF_INET, SOCK_STREAM, $proto)
or die "cannot open socket $!\n";
setsockopt(SOCKET, SOL_SOCKET, SO_REUSEADDR, 1)
or die "cannot make reusable $!\n";

# bind to a port followed by listen
bind( SOCKET, pack_sockaddr_in($port, inet_aton($server)))
or die "cannot bind to port $port! \n";

listen(SOCKET, 5) or die "listen: $!";
print "SERVER socket started on port $port\n";

# accept a connection
my $client_addr;
while ($client_addr = accept(NEW_SOCKET, SOCKET)) {
# send message to close connection
my $name = gethostbyaddr($client_addr, AF_INET );
print NEW_SOCKET "new socket welcome";
print "Connection established $name\n";
close NEW_SOCKET;
}

Client-side Method

connect() call -connect( SOCKET, ADDRESS );

Client-side Socket Script Example


!/usr/bin/perl -w
# Filename : clientsocket.pl

use strict;
use Socket;

# start host and port
my $host = shift || 'localhost';
my $port = shift || 7999;
my $server = "localhost"; # Host IP address of the server

# create the socket and connect to the port
socket(SOCKET,PF_INET,SOCK_STREAM,(getprotobyname('tcp'))[2])
or die "Cannot create a socket $!\n";
connect( SOCKET, pack_sockaddr_in($port, inet_aton($server)))
or die "Cannot connect to port $port! \n";

my $line;
while ($line = ) {
print "$line\n";
}
close SOCKET or die "close: $!";

Relevant Perl Functions

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