#!/usr/local/bin/perl

use feature qw/say/;
use strict;
use warnings;

open my $FASTAFILE, "<", 'human_fold_25.txt'
    or die "Could not open file: $!";

my $sequence = ' ';
my $Ccount = 0;
my $Gcount = 0;
my $identifier = ' ';

while(my $line = <$FASTAFILE>) {

    chomp $line;
    next if $line =~ m/^\./;

    if ($line =~ /^>/) {
        $identifier = $line;
    } elsif ($line !~ /^\(/) {

        $sequence = $line;
        $Gcount = $Ccount = 0;

        my $sequencelength = length $sequence;
        my @nucleotides = split('', $sequence);

        foreach my $nuc (@nucleotides) {
            if ($nuc eq 'G') {
                $Gcount = $Gcount + 1;
            } elsif ($nuc eq 'C') {
                $Ccount = $Ccount + 1;
            }
        }

        my $GCcontent = ((($Gcount + $Ccount) / $sequencelength) * 100);
        say "$identifier, $GCcontent";

    }
}

close $FASTAFILE or die "Could not close file: $!";