Remove the read mate number from the end of read IDs in a Fastq file

remove-mate.pl

#!/usr/bin/env perl

use strict;
use warnings;

my $state = 0; # 0 = ID; 1 = sequence; 2 = repeat ID; 3 = quality
my $seqlen = 0;

while (<>) {
    chomp;
    if ($state == 0) {
        s|/[12]$||;
        $state = 1;
    } elsif ($state == 1) {
        if (/^\+/) {
            $state = 3; # Skips repeat ID entirely.
        } else {
            $seqlen += length;
        }
    } else {
        $seqlen -= length;
        $state = 0 if $seqlen == 0;
    }
    print;
    print "\n";
}