Perl join Function
last modified April 4, 2025
The Perl join function combines list elements into a single string.
It takes a separator and a list, returning the concatenated result.
join is the opposite of split and is essential for
string construction. It's efficient and works with any list-like data.
Basic join Usage
The simplest way to use join is with a separator and array.
#!/usr/bin/perl
use strict;
use warnings;
use v5.34.0;
my @words = ('apple', 'banana', 'cherry');
my $result = join(', ', @words);
print "Joined string: $result\n";
We join three fruits with a comma and space separator. The function combines array elements into one string.
$ ./basic.pl Joined string: apple, banana, cherry
Joining with Empty Separator
An empty separator concatenates elements without any characters between.
#!/usr/bin/perl
use strict;
use warnings;
use v5.34.0;
my @numbers = (1, 2, 3, 4);
my $combined = join('', @numbers);
print "Combined: $combined\n";
print "Length: ", length($combined), "\n";
This joins numbers directly together. The result is a single string of digits.
$ ./empty.pl Combined: 1234 Length: 4
Joining with Newlines
Using newline as separator creates multi-line strings from lists.
#!/usr/bin/perl
use strict;
use warnings;
use v5.34.0;
my @lines = ('First line', 'Second line', 'Third line');
my $text = join("\n", @lines);
print "Result:\n$text\n";
Each array element becomes a separate line. This is useful for file output.
$ ./newlines.pl Result: First line Second line Third line
Joining Hash Values
join can combine hash values after extracting them.
#!/usr/bin/perl
use strict;
use warnings;
use v5.34.0;
my %fruit_colors = (
apple => 'red',
banana => 'yellow',
grape => 'purple'
);
my $color_list = join(', ', values %fruit_colors);
print "Fruit colors: $color_list\n";
We extract hash values with values then join them. The order
of values is unpredictable.
$ ./hash.pl Fruit colors: yellow, red, purple
Complex Separators
Separators can be multi-character strings for complex formatting.
#!/usr/bin/perl
use strict;
use warnings;
use v5.34.0;
my @items = ('CPU', 'RAM', 'SSD', 'GPU');
my $separator = " | ";
my $specs = join($separator, @items);
print "Computer specs:\n$specs\n";
The pipe separator with spaces creates a readable list. This is common in console output.
$ ./complex.pl Computer specs: CPU | RAM | SSD | GPU
Joining with Variables
Variables can be used both as separators and list elements.
#!/usr/bin/perl use strict; use warnings; use v5.34.0; my $user = 'admin'; my $domain = 'example.com'; my $separator = '@'; my $email = join($separator, $user, $domain); print "Email: $email\n";
We construct an email address by joining username and domain. Variables provide flexibility.
$ ./variables.pl Email: admin@example.com
Joining Split Results
join often pairs with split for string processing.
#!/usr/bin/perl
use strict;
use warnings;
use v5.34.0;
my $csv = "one,two,three,four";
my @parts = split(',', $csv);
my $new_csv = join(';', @parts);
print "Original: $csv\n";
print "Modified: $new_csv\n";
We split a CSV string then rejoin with different separators. This is common in data conversion.
$ ./splitjoin.pl Original: one,two,three,four Modified: one;two;three;four
Best Practices
- Choose clear separators: Make joined strings readable.
- Pre-allocate for performance: Use join instead of concatenation in loops.
- Combine with map/grep: Process elements before joining.
- Watch for undef: Undefined elements become empty strings.
Source
This tutorial covered Perl's join function with practical
examples demonstrating its usage in string construction.
Author
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