open my $fh_output,'>>',$output or die "can't open file: $!";
    open my $fh_input_file1,'<',$input_file1 or die "can't open file: $!";
    open my $fh_input_file2,'<',$input_file2 or die "can't open file: $!";
     ...
            if ( $dec eq "y" ) {
                print "\nadded \n\n";
                ...
                print $fh_output "$sw \t $_ \n";
            }
    ...