Under the assumption that the strings you are looking for are always the values of the /locus_tag, it is better to load the values you are searching for into a hash to use the exists function in addition to a regex. So you could loop over your second file, extract the value of the /locus_tag and if it exists in the hash, print the next line. 

use strict;
use warnings;

my %hashOfVals;
open(my $tmp, "<", "NC_001903.gbk.txt") || die "Could not open $!";
undef @hashOfVals{map {chomp; $_} <$tmp>};
close($tmp);

open(my $tmpFile, "<", "cp26_diffexpr.txt") || die "Could not open $!"
+;
my @arrayFromCSV = <$tmpFile>;
chomp @arrayFromCSV;
close($tmpFile);

for (0..$#arrayFromCSV-1) {
    print "$1: $arrayFromCSV[$_+1]\n" 
        if $arrayFromCSV[$_] =~ /locus_tag="(.*)"/ and exists $hashOfV
+als{$1};
}

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In reply to Re: Need Help with Maybe a Regex Issue by hdb
in thread Need Help with Maybe a Regex Issue by sharkbait

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