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$ cat infile1.txt
line1
...
line3
line4
line2

#!/usr/bin/perl
use strict;
...
map { chomp; $hash{ $_ }++ } <IN>;
close($in);
print Dumper \%hash;

Output:
$VAR1 = {
...
          'line4' => 1,
          'line1' => 2
        };