Re: How to I check if a value is present in an array?

[rjt]

This seems rather similar to how to refer the index of an array to another array of the same length you asked a little over an hour ago, which already has several replies.

This one is a bit different, though, so here's what I would suggest. Since you will be looping over @gl for every item in @genes, put @gl in a hash (only the keys matter). You can use a hash slice:

    my %gl; @gl{@gl} = undef;

Then, the lookup is both simple and efficient:

    say for grep { exists $gl{$_} } @genes;

Complete example:

#!/usr/bin/env perl

use 5.012;
use warnings FATAL => 'all';

my @genes = (qw<one two three four>);
my @gl    = (qw<    two three      five six>);

my %gl; @gl{@gl} = undef; # Efficient lookups
say for grep { exists $gl{$_} } @genes;

Output:

two
three