my $file1 = "file1.txt";
my $file2 = "file2.txt";
my $file3 = "output.txt";

my $match = 0;

# Open the files for reading
open( FILE1, $file1 );
open( FILE2, $file2 );

while ( <FILE1> ) {
    my $string1 = $_;
    my $string2 = <FILE2>;

    print "$counter: $string1\n$string2\n\n\n";

    ++$match if ( $string1 eq $string2 );
}

close FILE1;
close FILE2;

if ( $match ) {
    open( FILE3, '> $file3' );
    print FILE3 "$match lines matched\n";
    close FILE3;
}