Perl chr Function

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This short Perl chr Tutorial will show you how to use this function in your scripts. This function is used to convert ASCII or Unicode values into their equivalent characters. The reverse of this function is the ord function which is used to convert a character to its ASCII or Unicode value.

Two syntax forms are available for the Perl chr function:

chr EXPR 
chr

This function:
  • has as argument a number or an expression which after evaluation will return a number
  • returns the character represented by the EXPR
If the Perl chr Function has no argument, the $_ is used instead.


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A simple example


See the following simple example of the chr function usage:

#!/usr/local/bin/perl

use strict;
use warnings;

print chr(65), "\n";
# it displays: A

print chr(0x41), "\n";
# it displays: A

my $str = chr(0x263a);
print length $str, "\n";
# it displays: 1 (character context)

{
  use bytes;
  print length $str, "\n";
  # it displays: 3 (bytes pragma context)
}

The line of code:

my $str = chr(0x263a);

initializes the $str with the 0x263a hexadecimal value which is a Unicode smiley face. Please note that the length of a single character held in $str is 1 because the length function acts in a character context. However, if the length is calculated within the scope of the bytes pragma, the result will be returned in bytes – in our example 3.

Instead of using the Perl chr function to initialize a string with Unicode characters, you can use hexadecimal escapes. A hexadecimal escape begins with \x and it is either followed by a two digit hexadecimal number (for example "\x30" is "0") or a hexadecimal of arbitrary length included in curly braces (\x{263a}).

So, you could write:

my $str = "\x{263a}";

instead of:

my $str = chr(0x263a);

Convert an ASCII code string into a character string


The following example shows you how to use the Perl chr function in conjunction with the split, map and join functions.

#!/usr/local/bin/perl

use strict;
use warnings;

# initialize a string 
my $str = "72 101 108 108 111 32 87 111 114 108 100 33";

# split the string into an array of characters
my @array = split / /,$str;

# converts the elements of the array into characters
@array = map (chr, @array);

# join the elements of the array into the $str
$str = join "",@array;

# finnaly, print the string
print "$str\n";
# it outputs: Hello World!


I want to make a few considerations about this code:
  • the $str scalar variable is initialized with a sequence of ASCII codes, separated by space
  • the split function is used with the space pattern (" ") delimiter and it will return an array with the ASCII codes
  • the map function will run the Perl chr function for each element of the @array; at each iteration step the current element is assigned in turn to $_ and next the chr function will act against the special variable $_; the map function returns the same array but having characters as elements
  • the @array elements will be concatenated into $str by using the join function without any delimiter ("")
The one-line map function:

@array = map (chr, @array);

can be rewritten with any of the following code lines:

@array = map (chr $_, @array);
@array = map { chr } @array;
@array = map { chr $_ } @array;

By the way, calling the map function with the expression syntax form is faster than calling it with the block syntax form.

A quicker alternative to do this is by using the pack function, as in the following example:

#!/usr/local/bin/perl

use strict;
use warnings;

my $str = "72 101 108 108 111 32 87 111 114 108 100 33";

# split the string into an array of characters
my @array = split / /,$str;
$str = pack("C*", @array);
print "$str\n";
# it displays: Hello World!

Please note that there is an important difference between the Perl chr and the pack functions. Whereas chr works on characters, the pack "C" function works on bytes. If you use the standard ASCII character set, you’ll get the same result. But if you use Unicode, the pack function will behave the same meanwhile the Perl chr function will deal with the full Unicode character, which may be longer than 1 byte.

Convert a hexadecimal string into a character string


See the following snippet code:

#!/usr/local/bin/perl

use strict;
use warnings;

my $str = "48656c6c6f20576f726c6421";

$str =~ s/([a-fA-F0-9][a-fA-F0-9])/chr(hex($1))/eg;
print $str, "\n";
# it displays: Hello World!

In the above example:
  • the $str scalar variable is initialized with a few 2-digit hexadecimal values
  • in order to convert the hex string stored in $str to a character string the s/// substitution operator is used:
    • ([a-fA-F0-9][a-fA-F0-9]) match any two hexadecimal digits and store them in $1 - the using of round parentheses allow us to store the matched expression in the special variable named $1 and if you have more parentheses, the expression included in the second parenthesis will be assigned to $2, and so on
    • chr(hex($1) represents the replacement argument of the substitution operator; the hex function will convert the hexadecimal string stored in $1 in its decimal corresponding value and it will return this value; the chr function will return the character represented by the numeric value returned by the hex function
    • e is a modifier and it tells the regex engine to treat the replacement field as Perl code
    • g is a modifier and tells the regex engine to repeatedly apply the substitution for all the characters of the string, starting with the first one
Finally, the content of the $str is printed, so the output will be:

Hello World!

If you want to download the Perl chr script with all the above examples included, please click here: Script download


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Table of Contents:

A Perl Script
Install Perl
Running Perl
Perl Data Types
Perl Variables
Perl Operators
Perl Lists
Perl Arrays
    Array Size
    Array Length
Perl Hashes
Perl Statements
    Perl if
    Perl unless
    Perl switch
    Perl while
    Perl do-while
    Perl until
    Perl do-until
    Perl for
    Perl foreach
Built-in Perl Functions
    Functions by Category
        String Functions
        Regular Expressions and Pattern Matching
        List Functions
        Array Functions
        Hash Functions
        Miscellaneous Functions
    Functions in alphabetical order
        chomp
        chop
        chr (more)
        crypt
        defined
        delete
        each
        exists
        grep
        hex
        index
        join
        keys
        lc
        lcfirst
        length
        map
        oct
        ord
        pack
        pop
        push
        q
        qq
        qw
        reverse
        rindex
        scalar
        shift
        sort
        splice
        split
        sprintf
        substr
        tr
        uc
        ucfirst
        undef
        unpack
        unshift
        values

return from Perl chr function to Perl Basics



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