=head1 DESCRIPTION

Compare 2 text files

=cut

$usage = "perl -w ... file1  [ file2 ]";

=head1 COMMAND LINE PARAMETERS

 perl -w ... file1  [ file2 ]


=cut

sub errx {
	print STDERR $_[0], "\n";
	exit 1;
}

sub comparelines {
	my $a = shift;
	my $b = shift;
	my $len1 = length $a;
	my $len2 = length $b;
	print STDERR "lines lengths: $len1, $len2\n";
	
	CHAR: for (my $i =0; $i < $len1 && $i < $len2; $i++) {
		my ($cc,$dd) = (substr($a,$i,1), substr($b,$i,1));
		if ($cc eq $dd) {
			print $cc;
		} else {
			printf STDERR "\nmismatch at char %d: '%s' (%d) and '%s' (%d)\n",
				$i+1, $cc, ord($cc), $dd, ord($dd);
			
			last CHAR;
		}
	}
}


##
## get the command-line parameters
##
$afile = shift or &errx($usage);
if (0) { 
 while (@ARGV+0 && $ARGV[0] =~ /^-/) {
	my $aa = $ARGV[0];
	last if $aa eq '--';
	if ($aa eq '--foo') {
		$foo = $ARGV[1];
		shift @ARGV;
		shift @ARGV;
	}
	elsif ($aa eq '-d') {
		$debug = 1;
		shift @ARGV;
	} else {
		print STDERR "bad arg: $aa\n";
		&errx($usage);
	}
 }
 print "foo=$foo";
}


##
## read in the first file
##
open(AFILE, "< $afile") or &errx("cannot open $afile: $!");

@alines = ();
ALINE: while (<AFILE>) {
	print STDERR "ALINE: $_" if $debug;
	push @alines, $_;
}
printf("file1: %d lines\n", 0+@alines);

close(AFILE);

##
## get the second file
##
$chomped = 0;
$lineno = 0;
DLINE: while (<>) {
	$lineno++;
	chomp if $chomped;
	#print STDERR "line $.\n";
	if ($lineno > (0+@alines)) {
		errx "line $lineno: second file is bigger";
	}
	if ($_ ne $alines[$lineno-1]) {
		print STDERR "file1: ", $alines[$lineno-1], "\n";
		print STDERR "file2: ", $_, "\n";
		comparelines $alines[$lineno-1], $_;
		errx "line $lineno: mismatch";
	}
}
printf("file2: %d lines\n", $lineno);

exit 0;