In this part of your code

open(FH,"file.txt");
while(<FH>)
{
        $var = $_;
        print "$var\n";
}
close(FH);
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$var will only be set to the very last line of your file, not the whole file.
Replace $var = $_; with $var .= $_; so that it contains the whole file. Also add a line like my $var; before the while (<FH>) line.
Those lines should look like this:

open(FH,"file.txt");
my $var;
while(<FH>)
{
        $var .= $_;
}
close(FH);
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