In my shop, we use cvs. To compare the differences between two versions, I used to do:

cvs diff -y -r v1 -r v2 >out.txt 2>&1

This works fine with comparing two source files. However when I compare two directories, the output file becomes really big, and even worse, the output fom cvs is a mixtrue of differences and common lines, so the differences are just buried among all those common lines.

I want to extra those real differences.

For those lines really different between two versions, its 63th column is one of those three chars: |, >, or <.

The part caused me a little bit effort is to translate \t into blanks, as I have to calculate the number of blanks. (\t is not always 8 blanks, but rather padding up to the next 8's multiplier)

To use this program, do this:

real_diff.pl out

It would create a file called out.rl, which only contains those lines that are really different between two versions. 
real_diff.pl

#!/usr/bin/perl

use strict;
use warnings;

my $directory;
if (!$ARGV[0]) {
    die "Usage: real_diff.pl directory_name\n";
} else {
    $directory = $ARGV[0];
}

open(DIFF_FILE, "<", "$directory.txt") || die "There is no diff file f
+or directory $directory\n";
my @lines = <DIFF_FILE>;
close(DIFF_FILE);

print "Now creating real diff file $directory.rl ...\n";
my $prev_line;
my $current_file;
open(REAL_DIFF, ">", "$directory.rl");
for (0 .. $#lines) {
    my $line = $lines[$_];
    my $out_line = "";
    for (my $i = 0; $i < length($line); $i ++) {
        if (substr($line, $i, 1) eq "\t") {
            $out_line .= " " x (8 - length($out_line) % 8);
        } else {
            $out_line .= substr($line, $i, 1);
        }
    }
    if ($out_line =~ m/^RCS file: (.*?),/) {
        $current_file = $1;
    }
    if ($out_line =~ m/^.{62}[<|>|\|]/) {
        if (!$prev_line || ($_ > $prev_line + 1)) {
            print REAL_DIFF "=========================================
+=============================\n";
            print REAL_DIFF "line number in $directory.txt: " , $_ + 1
+, "\n";
            print REAL_DIFF "Source file name: $current_file\n\n";
        }
        print REAL_DIFF $out_line;
        $prev_line = $_;
    }
}
close(REAL_DIFF);

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In reply to extract useful infos from cvs diff output by pg

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