On Wed, 2011-01-12 at 15:00 +0000, Matthew King wrote: > GNU diff has an option described thusly: > > -I RE --ignore-matching-lines=RE > Ignore changes whose lines all match RE. > > Fantastic, says you, now I can compare two files and see only if lines > which aren't comments differ by telling diff to ignore lines which > begin with a '#'. > > No, says GNU, that is useful functionality which would be the logical > extension of *all* the other 'ignore' options diff accepts. What -I RE > will do instead is indicate that *the entire file* does not differ iff > *all differing lines* match the regular expression. In the highly > likely situation that lines which match your expression differ *and* > lines which don't match differ, you will see every line of difference, > whether it matches or not. > > Hate.
I don't think you read it literally enough. It applies to a chunk not the whole file. It ignores chunks where all changed lines match the regexp. eg. diff -u a b --- a 2011-01-13 02:10:53.000000000 +1030 +++ b 2011-01-13 02:11:14.000000000 +1030 @@ -1,4 +1,4 @@ -abc +abd abc ddd ddd @@ -7,5 +7,5 @@ eee eee ddd -ddd +ddc ddd # diff -u -I b a b --- a 2011-01-13 02:10:53.000000000 +1030 +++ b 2011-01-13 02:11:14.000000000 +1030 @@ -7,5 +7,5 @@ eee eee ddd -ddd +ddc ddd It's still hateful though because if it behaved how you expected it to it'd be a lot more useful. It's easy to see how it was simpler to implement the way it does work though, so the option is really a bad hack. Cheers, Martin
