#!/usr/bin/perl -l
use strict;
use warnings;

print "If an array element is a line number and a base together as a string:";

my %positions;

for my $line (split /\n/, <<'END') 
1 ACAC
2 AGAC
3 AGTC
4 ACCA
END

{
	next if $line =~ /[GT]/;
	my ($number, $bases ) = split / /, $line;
	$positions{$number} = $bases;	
}

for my $number ( sort keys %positions )
{
	print "$number => $positions{$number}";
	print "Just print a number $number";
}

print "If there is an array element for a line number and for a base:";

my @array = ( qw (1 ACAC 2 AGAC 3 AGTC 4 ACCA) );
%positions = ();
for (my $i = 0; $i < @array; $i +=2 )
{
	my ($number, $bases ) = @array[$i, $i+1];
	next if $bases =~ /[GT]/;
	$positions{$number} = $bases;
}

for my $number (sort keys %positions)
{
	print "$number => $positions{$number}";
	print "Just print a number $number";
}