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Perl

Perl Cheat Sheet - 快速参考指南，收录常用语法、命令与实践。

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Getting Started

Unix and Linux Installation

Open a Web browser and go to https://www.perl.org/get.html.
Follow the link to download zipped source code available for Unix/Linux.
Download perl-5.x.y.tar.gz file and issue the following commands at $ prompt.

SHELL

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$tar -xzf perl-5.x.y.tar.gz
$cd perl-5.x.y
$./Configure -de
$make
$make test
$make install

Windows Installation

Follow the link for the Strawberry Perl installation on Windows http://strawberryperl.com
Download either 32bit or 64bit version of installation.
Run the downloaded file by double-clicking it in Windows Explorer. This brings up the Perl install wizard, which is really easy to use. Just accept the default settings, wait until the installation is finished, and you're ready to roll!

Macintosh Installation

Open a Web browser and go to https://www.perl.org/get.html.
Follow the link to download zipped source code available for Mac OS X.
Download perl-5.x.y.tar.gz file and issue the following commands at $ prompt

SHELL

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$tar -xzf perl-5.x.y.tar.gz
$cd perl-5.x.y
$./Configure -de
$make
$make test
$make install

Running Perl

SHELL

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# Unix/Linux
$perl  -e <perl code>
# Windows/DOS
C:>perl -e <perl code>

Available command line options

Option	Description
-d[:debugger]	Runs program under debugger
-Idirectory	Specifies @INC/#include directory
-T	Enables tainting warnings
-U	Allows unsafe operations
-w	Enables many useful warnings
-W	Enables all warnings
-X	Disables all warnings
-e program	Runs Perl script sent in as program
file	Runs Perl script from a given file

Script from the Command-line

SHELL

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# Unix/Linux
$perl  script.pl
# Windows/DOS
C:>perl script.pl

First Perl Program

SHELL

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$perl -e 'print "Hello World\n"'

# #!/usr/bin/perl

# This will print "Hello, World"
print "Hello, world\n";
$chmod 0755 hello.pl
$./hello.pl

Comments in Perl

PERL

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# This is a comment in perl
=begin comment
This is all part of multiline comment.
You can use as many lines as you like
These comments will be ignored by the
compiler until the next =cut is encountered.
=cut

Whitespaces in Perl

PERL

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#!/usr/bin/perl

# This would print with a line break in the middle
print "Hello
          world\n";
#output
#Hello
#         world

Single and Double Quotes in Perl

PERL

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#!/usr/bin/perl

print "Hello, world\n";
print 'Hello, world\n';

#Hello, world
#Hello, world\n$

Datatypes

Creating Variables

PERL

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$age = 25;             # An integer assignment
$name = "John Paul";   # A string
$salary = 1445.50;     # A floating point

Scalar Variables

PERL

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#!/usr/bin/perl

$age = 25;             # An integer assignment
$name = "John Paul";   # A string
$salary = 1445.50;     # A floating point

print "Age = $age\n";
print "Name = $name\n";
print "Salary = $salary\n";

Array Variables

PERL

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#!/usr/bin/perl

@ages = (25, 30, 40);
@names = ("John Paul", "Lisa", "Kumar");

print "\$ages[0] = $ages[0]\n";
print "\$ages[1] = $ages[1]\n";
print "\$ages[2] = $ages[2]\n";
print "\$names[0] = $names[0]\n";
print "\$names[1] = $names[1]\n";
print "\$names[2] = $names[2]\n";

Hash Variables

PERL

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#!/usr/bin/perl

%data = ('John Paul', 45, 'Lisa', 30, 'Kumar', 40);

print "\$data{'John Paul'} = $data{'John Paul'}\n";
print "\$data{'Lisa'} = $data{'Lisa'}\n";
print "\$data{'Kumar'} = $data{'Kumar'}\n";

Variable Context

PERL

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#!/usr/bin/perl

@names = ('John Paul', 'Lisa', 'Kumar');

@copy = @names;
$size = @names;

print "Given names are : @copy\n";
print "Number of names are : $size\n";

Numeric Scalars

PERL

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#!/usr/bin/perl

$integer = 200;
$negative = -300;
$floating = 200.340;
$bigfloat = -1.2E-23;

# 377 octal, same as 255 decimal
$octal = 0377;

# FF hex, also 255 decimal
$hexa = 0xff;

print "integer = $integer\n";
print "negative = $negative\n";
print "floating = $floating\n";
print "bigfloat = $bigfloat\n";
print "octal = $octal\n";
print "hexa = $hexa\n";

String Scalars

PERL

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#!/usr/bin/perl

$var = "This is string scalar!";
$quote = 'I m inside single quote - $var';
$double = "This is inside single quote - $var";

$escape = "This example of escape -\tHello, World!";

print "var = $var\n";
print "quote = $quote\n";
print "double = $double\n";
print "escape = $escape\n";

Scalar Operations

PERL

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#!/usr/bin/perl

$str = "hello" . "world";       # Concatenates strings.
$num = 5 + 10;                  # adds two numbers.
$mul = 4 * 5;                   # multiplies two numbers.
$mix = $str . $num;             # concatenates string and number.

print "str = $str\n";
print "num = $num\n";
print "mul = $mul\n";
print "mix = $mix\n";

Multiline Strings

PERL

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#!/usr/bin/perl

$string = 'This is
a multiline
string';

print "$string\n";

##########################
print <<EOF;
This is
a multiline
string
EOF

V-Strings

PERL

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#!/usr/bin/perl

$smile  = v9786;
$foo    = v102.111.111;
$martin = v77.97.114.116.105.110;

print "smile = $smile\n";
print "foo = $foo\n";
print "martin = $martin\n";

Special Literals

PERL

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#!/usr/bin/perl

print "File name ". __FILE__ . "\n";
print "Line Number " . __LINE__ ."\n";
print "Package " . __PACKAGE__ ."\n";

# they can not be interpolated
print "__FILE__ __LINE__ __PACKAGE__\n";

Sequential Number Arrays

PERL

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#!/usr/bin/perl

@var_10 = (1..10);
@var_20 = (10..20);
@var_abc = (a..z);

print "@var_10\n";   # Prints number from 1 to 10
print "@var_20\n";   # Prints number from 10 to 20
print "@var_abc\n";  # Prints number from a to z

Array Size

PERL

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#!/usr/bin/perl

@array = (1,2,3);
$array[50] = 4;

$size = @array;
$max_index = $#array;

print "Size:  $size\n";
print "Max Index: $max_index\n";

Array oparationns

Adding and Removing Elements in Array

types	Description
push @ARRAY, LIST	Pushes the values of the list onto the end of the array.
pop @ARRAY	Pops off and returns the last value of the array.
shift @ARRAY	Shifts the first value of the array off and returns it, shortening the array by 1 and moving everything down.
unshift @ARRAY, LIST	Prepends list to the front of the array, and returns the number of elements in the new array.

Array oparations

PERL

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#!/usr/bin/perl

# create a simple array

@coins = ("Quarter","Dime","Nickel");
print "1. \@coins = @coins\n";

# add one element at the end of the array

push(@coins, "Penny");
print "2. \@coins = @coins\n";

# add one element at the beginning of the array

unshift(@coins, "Dollar");
print "3. \@coins = @coins\n";

# remove one element from the last of the array.

pop(@coins);
print "4. \@coins = @coins\n";

# remove one element from the beginning of the array.

shift(@coins);
print "5. \@coins = @coins\n";

Slicing Array Elements

PERL

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#!/usr/bin/perl

@days = qw/Mon Tue Wed Thu Fri Sat Sun/;

@weekdays = @days[3,4,5];

print "@weekdays\n";

Replacing Array Elements

PERL

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#!/usr/bin/perl

@nums = (1..20);
print "Before - @nums\n";

splice(@nums, 5, 5, 21..25);
print "After - @nums\n";

Transform Strings to Arrays

PERL

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#!/usr/bin/perl

# define Strings

$var_string = "Rain-Drops-On-Roses-And-Whiskers-On-Kittens";
$var_names = "Larry,David,Roger,Ken,Michael,Tom";

# transform above strings into arrays.

@string = split('-', $var_string);
@names = split(',', $var_names);

print "$string[3]\n";  # This will print Roses
print "$names[4]\n"; # This will print Michael

Transform Arrays to Strings

PERL

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#!/usr/bin/perl

# define Strings
$var_string = "Rain-Drops-On-Roses-And-Whiskers-On-Kittens";
$var_names = "Larry,David,Roger,Ken,Michael,Tom";

# transform above strings into arrays.
@string = split('-', $var_string);
@names  = split(',', $var_names);

$string1 = join( '-', @string );
$string2 = join( ',', @names );

print "$string1\n";
print "$string2\n";

Sorting Arrays

PERL

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#!/usr/bin/perl

# define an array
@foods = qw(pizza steak chicken burgers);
print "Before: @foods\n";

# sort this array
@foods = sort(@foods);
print "After: @foods\n";

The $[ Special Variable

PERL

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#!/usr/bin/perl

# define an array
@foods = qw(pizza steak chicken burgers);
print "Foods: @foods\n";

# Let's reset first index of all the arrays.
$[ = 1;

print "Food at \@foods[1]: $foods[1]\n";
print "Food at \@foods[2]: $foods[2]\n";

Merging Arrays

PERL

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#!/usr/bin/perl

@odd = (1,3,5);
@even = (2, 4, 6);

@numbers = (@odd, @even);

print "numbers = @numbers\n";

Selecting Elements from Lists

PERL

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#!/usr/bin/perl

@list = (5,4,3,2,1)[1..3];

print "Value of list = @list\n";

Accessing Hash Elements

PERL

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#!/usr/bin/perl

%data = ('John Paul' => 45, 'Lisa' => 30, 'Kumar' => 40);

print "$data{'John Paul'}\n";
print "$data{'Lisa'}\n";
print "$data{'Kumar'}\n";

Extracting Slices

PERL

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#!/uer/bin/perl


%data = (-JohnPaul => 45, -Lisa => 30, -Kumar => 40);

@array = @data{-JohnPaul, -Lisa};

print "Array : @array\n";

Extracting Keys and Values

PERL

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#!/usr/bin/perl

%data = ('John Paul' => 45, 'Lisa' => 30, 'Kumar' => 40);

@names = keys %data;

print "$names[0]\n";
print "$names[1]\n";
print "$names[2]\n";

Getting Hash Size

PERL

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#!/usr/bin/perl

%data = ('John Paul' => 45, 'Lisa' => 30, 'Kumar' => 40);

@keys = keys %data;
$size = @keys;
print "1 - Hash size:  is $size\n";

@values = values %data;
$size = @values;
print "2 - Hash size:  is $size\n";

Add and Remove Elements in Hashes

PERL

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#!/usr/bin/perl

%data = ('John Paul' => 45, 'Lisa' => 30, 'Kumar' => 40);
@keys = keys %data;
$size = @keys;
print "1 - Hash size:  is $size\n";

# adding an element to the hash;
$data{'Ali'} = 55;
@keys = keys %data;
$size = @keys;
print "2 - Hash size:  is $size\n";

# delete the same element from the hash;
delete $data{'Ali'};
@keys = keys %data;
$size = @keys;
print "3 - Hash size:  is $size\n";

Control Flow

if-else

PERL

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#!/usr/bin/perl

# Perl program to illustrate
# Decision-Making statements

$a = 10;
$b = 15;

# if condition to check
# for even number
if($a % 2 == 0 )
{
	printf "Even Number";
}

# if-else condition to check
# for even number or odd number
if($b % 2 == 0 )
{
	printf "\nEven Number";
}
else
{
	printf "\nOdd Number";
}

The ? : Operator

PERL

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#!/usr/local/bin/perl

$name = "Ali";
$age = 10;

$status = ($age > 60 )? "A senior citizen" : "Not a senior citizen";

print "$name is  - $status\n";

for loop

PERL

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#!/usr/bin/perl

# Perl program to illustrate
# the use of for Loop

# for loop
print("For Loop:\n");
for ($count = 1 ; $count <= 3 ; $count++)
{
	print "GeeksForGeeks\n"
}

foreach loop

PERL

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#!/usr/bin/perl

# Perl program to illustrate
# the use of foreach Loop

# Array
@data = ('GEEKS', 4, 'GEEKS');

# foreach loop
print("For-each Loop:\n");
foreach $word (@data)
{
	print ("$word ");
}

while and do-while

PERL

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#!/usr/bin/perl

# Perl program to illustrate
# the use of foreach Loop

# while loop
$count = 3;

print("While Loop:\n");
while ($count >= 0)
{
	$count = $count - 1;
	print "GeeksForGeeks\n";
}

print("\ndo...while Loop:\n");
$a = 10;

# do..While loop
do {

	print "$a ";
	$a = $a - 1;
} while ($a > 0);

Object Oriented Programming

Class and object

PERL

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#!/usr/bin/perl

# Perl Program for creation of a
# Class and its object
use strict;
use warnings;

package student;

# constructor
sub student_data
{

	# shift will take package name 'student'
	# and assign it to variable 'class'
	my $class_name = shift;
	my $self = {
				'StudentFirstName' => shift,
				'StudentLastName' => shift
			};
	# Using bless function
	bless $self, $class_name;

	# returning object from constructor
	return $self;
}

# Object creating and constructor calling
my $Data = student_data student("Geeks", "forGeeks");

# Printing the data
print "$Data->{'StudentFirstName'}\n";
print "$Data->{'StudentLastName'}\n";

Subroutines

PERL

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#!/usr/bin/perl

# Perl Program to demonstrate the
# subroutine declaration and calling

# defining subroutine
sub ask_user
{
	print "Hello Geeks!\n";
}

# calling subroutine
# you can also use
# &ask_user();
ask_user();

Modules and Packages

PERL

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#!/usr/bin/perl

# Using the Package 'Calculator'
use Calculator;

print "Enter two numbers to multiply";

# Defining values to the variables
$a = 5;
$b = 10;

# Subroutine call
Calculator::multiplication($a, $b);

print "\nEnter two numbers to divide";

# Defining values to the variables
$a = 45;
$b = 5;

# Subroutine call
Calculator::division($a, $b);

References

PERL

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# Perl program to illustrate the
# Referencing and Dereferencing
# of an Array

# defining an array
@array = ('1', '2', '3');

# making an reference to an array variable
$reference_array = \@array;

# Dereferencing
# printing the value stored
# at $reference_array by prefixing
# @ as it is a array reference
print @$reference_array;

Regular Expression

PERL

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# Perl program to demonstrate
# the m// and =~ operators

# Actual String
$a = "GEEKSFORGEEKS";

# Prints match found if
# its found in $a
if ($a =~ m[GEEKS])
{
	print "Match Found\n";
}

# Prints match not found
# if its not found in $a
else
{
	print "Match Not Found\n";
}

File Handling

PERL

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# Opening the file
open(fh, "GFG2.txt") or die "File '$filename' can't be opened";

# Reading First line from the file
$firstline = <fh>;
print "$firstline\n";

File Test Operators

PERL

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#!/usr/bin/perl

# Using predefined modules
use warnings;
use strict;

# Providing path of file to a variable
my $filename = 'C:\Users\GeeksForGeeks\GFG.txt';

# Checking for the file existence
if(-e $filename)
{

	# If File exists
	print("File $filename exists\n");
}

else
{

	# If File doesn't exists
	print("File $filename does not exists\n");
}

Working with Excel Files

PERL

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#!/usr/bin/perl
use Excel::Writer::XLSX;

my $Excelbook = Excel::Writer::XLSX->new( 'GFG_Sample.xlsx' );
my $Excelsheet = $Excelbook->add_worksheet();

$Excelsheet->write( "A1", "Hello!" );
$Excelsheet->write( "A2", "GeeksForGeeks" );
$Excelsheet->write( "B1", "Next_Column" );

$Excelbook->close;

Reading from an Excel File:

PERL

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use 5.016;
use Spreadsheet::Read qw(ReadData);
my $book_data = ReadData (‘new_excel.xlsx');
say 'A2: ' . $book_data->[1]{A2};

Error Handling

PERL

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if(open(DATA, $file)) {
   ...
} else {
   die "Error: Couldn't open the file - $!"
}
#example
open(DATA, $file) || die "Error: Couldn't open the file $!";

example

unless(chdir("/etc")) { die "Error: Can't change directory - $!"; } ##example print(exists($hash{value}) ? 'There' : 'Missing',"\n");

CODE

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The warn Function

PERL

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chdir('/etc') or warn "Can't change directory";

The die function

PERL

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chdir('/etc') or die "Can't change directory";

Errors within Modules

PERL

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package T;

require Exporter;
@ISA = qw/Exporter/;
@EXPORT = qw/function/;
use Carp;

sub function {
   warn "Error in module!";
}
1;
#use T;
#function();
# all below code call the funtion

The carp Function

PERL

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package T;

require Exporter;
@ISA = qw/Exporter/;
@EXPORT = qw/function/;
use Carp;

sub function {
   carp "Error in module!";
}
1;

The cluck Function

PERL

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package T;

require Exporter;
@ISA = qw/Exporter/;
@EXPORT = qw/function/;
use Carp qw(cluck);

sub function {
   cluck "Error in module!";
}
1;

The croak Function

PERL

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package T;

require Exporter;
@ISA = qw/Exporter/;
@EXPORT = qw/function/;
use Carp;

sub function {
   croak "Error in module!";
}
1;

The confess Function

PERL

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package T;

require Exporter;
@ISA = qw/Exporter/;
@EXPORT = qw/function/;
use Carp;

sub function {
   confess "Error in module!";
}
1;

Date and Time

Current Date and Time

PERL

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#!/usr/local/bin/perl

@months = qw( Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec );
@days = qw(Sun Mon Tue Wed Thu Fri Sat Sun);

($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime();
print "$mday $months[$mon] $days[$wday]\n";
#or
#!/usr/local/bin/perl

$datestring = localtime();
print "Local date and time $datestring\n";

GMT Time

PERL

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#!/usr/local/bin/perl

$datestring = gmtime();
print "GMT date and time $datestring\n";

Format Date and Time

PERL

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#!/usr/local/bin/perl

($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = localtime();

printf("Time Format - HH:MM:SS\n");
printf("%02d:%02d:%02d", $hour, $min, $sec);

Epoch time

PERL

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#!/usr/local/bin/perl

$epoc = time();

print "Number of seconds since Jan 1, 1970 - $epoc\n";
#or
#!/usr/local/bin/perl

$datestring = localtime();
print "Current date and time $datestring\n";

$epoc = time();
$epoc = $epoc - 24 * 60 * 60;   # one day before of current date.

$datestring = localtime($epoc);
print "Yesterday's date and time $datestring\n";

POSIX Function strftime()

Specifier	Replaced by	Example
%a	Abbreviated weekday name	Thu
%A	Full weekday name	Thursday
%b	Abbreviated month name	Aug
%B	Full month name	August
%c	Date and time representation	Thu Aug 23 14:55:02 2001
%C	Year divided by 100 and truncated to integer (00-99)	20
%d	Day of the month, zero-padded (01-31)	23
%D	Short MM/DD/YY date, equivalent to %m/%d/%y	08/23/01
%e	Day of the month, space-padded ( 1-31)	23
%F	Short YYYY-MM-DD date, equivalent to %Y-%m-%d	2001-08-23
%g	Week-based year, last two digits (00-99)	01
%G	Week-based year	2001
%h	Abbreviated month name (same as %b)	Aug
%H	Hour in 24h format (00-23)	14
%I	Hour in 12h format (01-12)	02
%j	Day of the year (001-366)	235
%m	Month as a decimal number (01-12)	08
%M	Minute (00-59)	55
%n	New-line character ('\n')
%p	AM or PM designation	PM
%r	12-hour clock time	02:55:02 pm
%R	24-hour HH:MM time, equivalent to %H:%M	14:55
%S	Second (00-61)	02
%t	Horizontal-tab character ('\t')
%T	ISO 8601 time format (HH:MM:SS), equivalent to %H:%M:%S	14:55
%u	ISO 8601 weekday as number with Monday as 1 (1-7)	4
%U	Week number with the first Sunday as the first day of week one (00-53)	33
%V	ISO 8601 week number (00-53)	34
%w	Weekday as a decimal number with Sunday as 0 (0-6)	4
%W	Week number with the first Monday as the first day of week one (00-53)	34
%x	Date representation	08/23/01
%X	Time representation	14:55:02
%y	Year, last two digits (00-99)	01
%Y	Year	2001
%z	ISO 8601 offset from UTC in timezone (1 minute = 1, 1 hour = 100)If timezone cannot be termined, no characters	+100
%Z	Timezone name or abbreviation If timezone cannot be termined, no characters	CDT
%%	A % sign	%

PERL

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#!/usr/local/bin/perl
use POSIX qw(strftime);

$datestring = strftime "%a %b %e %H:%M:%S %Y", localtime;
printf("date and time - $datestring\n");

# or for GMT formatted appropriately for your locale:
$datestring = strftime "%a %b %e %H:%M:%S %Y", gmtime;
printf("date and time - $datestring\n");

Perl

Getting Started

Datatypes

Array oparationns

Control Flow

Object Oriented Programming

example

Date and Time

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