open($fh1, $file1) or die "Can't open $file1";
open($fh2, $file2) or die "Can't open $file2";
+# print files to output so we know which is which
+print "-$file1\n";
+print "+$file2\n";
+
# buffer of matching lines for pre-diff context
my @precontext = ();
# number of post-diff matching lines remaining to print