grep doesn't do what you think. It returns a list of all elements where the search expression is true. The search expression in your case is $genes[$index], so if that's a true value, grep returns all the elements of @gl.

What you probably want to write instead is something like 

for my $current (@genes) {
    if (grep { $_ eq $current } @gl) {
         print $current;
    }
}

[download]

Though of course if either (or both) of these arrays is large, that is rather inefficient, and you might consider storing stuff in a hash in the first place.

Perl 6 - the future is here, just unevenly distributed

In reply to Re: How to I check if a value is present in an array? by moritz
in thread How to I check if a value is present in an array? by rocketperl

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