Perl String

Perl’s built-in string functions to manipulate strings.

1. Introduction to Perl strings

In Perl, a string is a sequence of characters surrounded by some kind of quotation marks. A string can contain ASCII, UNICODE, and escape sequences characters such as \n.

A Perl string has a length that depends on the amount of memory in your system, which is theoretically unlimited.

The following example demonstrates single and double-quoted strings.

my $s1 = "string with doubled-quotes";
my $s2 = 'string with single quote';

It is important to remember that the double-quoted string replaces variables inside it by their values, while the single-quoted string treats them as text. This is known as variable interpolation in Perl.

2. Perl string alternative delimiters

Besides the single and double quotes, Perl also allows you to use quote-like operators such as:

  • The q// acts like a single-quoted string.

  • The qq// acts like double-quoted string

You can choose any non-alphabetic and non-numeric characters as the delimiters, not only just characters //.

#!/usr/bin/perl
use warnings;
use strict;

my $s= q/"Are you learning Perl String today?" We asked./;
print($s ,"\n");

my $name = 'Jack';
my $s2 = qq/"Are you learning Perl String today?"$name asked./;
print($s2 ,"\n");
How it works

  • First, defined a single-quoted string variable with the quote-like operator q/. The string $s ends with /

  • Second, defined a double-quoted string with the quote-like operator qq/. In this case, we used the $name variable inside a string and it is replaced by its value, Jack

The following example demonstrates string with the ^ delimiter.

#!/usr/bin/perl
use warnings;
use strict;

my $s = q^A string with different delimiter ^;
print($s,"\n");

3. Perl string functions

Perl provides a set of functions that allow you to manipulate strings effectively. We cover the most commonly used string functions in the following section for your reference.

Perl string length

To find the number of characters in a string, you use the length() function.

my $s = "This is a string\n";
print(length($s),"\n"); #17
Changing cases of string

To change the cases of a string you use a pair of functions lc() and uc() that returns the lowercase and uppercase versions of a string.

my $s = "Change cases of a string\n";
print("To upper case:\n");
print(uc($s),"\n");

print("To lower case:\n");
print(lc($s),"\n");
Search for a substring inside a string

To search for a substring inside a string, you use index() and rindex() functions.

  • The index() function searches for a substring inside a string from a specified position and returns the position of the first occurrence of the substring in the searched string. If the position is omitted, it searches from the beginning of the string.

  • The rindex() function works like the index() function except it searches from the end of the string instead of from the beginning.

The following example demonstrates how to use the index() and rindex() functions:

#!/usr/bin/perl
use warnings;
use strict;

my $s = "Learning Perl is easy\n";
my $sub = "Perl";
my $p = index($s,$sub); # rindex($s,$sub);
print(qq\The substring "$sub" found at position "$p" in string "$s"\,"\n");
Get or modify substring inside a string

To extract a substring out of a string, you use the substr() function.

#!/usr/bin/perl
use warnings;
use strict;
# extract substring
my $s = "Green is my favorite color";
my $color  = substr($s, 0, 5);      # Green
my $end    = substr($s, -5);        # color

print($end,":",$color,"\n");

# replace substring
substr($s, 0, 5, "Red"); #Red is my favorite color
print($s,"\n");
Other useful Perl string functions

The following table illustrates other useful Perl string functions with their descriptions:

Function Description

chr

Return ASCII or UNICODE character of a number

crypt

Encrypts passwords in one way fashion

hex

Converts a hexadecimal string to the corresponding value

index

Searches for a substring inside a string returns position where the first occurrence of the substring found

lc

Returns a lowercase version of the string

length

Returns the number of characters of a string

oct

Converts a string to an octal number

ord

Returns the numeric value of the first character of a string

q/string/

Creates single-quoted strings

qq/string/

Creates double-quoted strings

reverse

Reverses a string

rindex

Searches for a substring from right to left

sprintf

Formats string to be used with print()

substr

Gets or modifies a substring in a string

uc

Returns the uppercase version of the string