You might be better of using the line count as the key, and line text as value...

#!/usr/bin/perl

use strict;

open IN, "$infile1" or die $!;

my $linecount = 0;
my %hash;

while (my $line = <IN>) {
    chomp $line;
    $linecount+=1;
    $hash{$linecount} = $line;
}
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