Using the Perl grep() function

Using the Perl grep() function

Introduction

The grep function is used to filter lists. The basic syntax is

    @out = grep { CODE } @in;

where CODE is some Perl code. For each element of @in, CODE is executed with $_ set to the element. If the code returns a true value, the element is placed in the output list; otherwise it is discarded.

Example 1

Say you have a list of strings, and want to keep only those with less than 8 characters.

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

    my @strs = qw(potatoes lemons apricots apples bananas ostriches flamingoes);
    my @short_strs = grep { length $_ < 8 } @strs;
    for my $str (@short_strs) {
        print "$str\n";
    }

This produces the output:

    lemons
    apples
    bananas

Example 2

What if you have a list of files, and want only those ending in .html? We can use grep together with a regular expression:

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

    my @files = qw(index.html test.html test.txt Makefile home.html help.doc README.txt);
    my @html_files = grep { /\.html$/ } @files;
    for my $file (@html_files) {
        print "$file\n";
    }

This produces the output:

    index.html
    test.html
    home.html

See also

    perldoc -f grep