Re: [gentoo-user] [OT] confusing RE doesn't work in diff

[Mariusz Pękala]

On 2005-07-27 09:43:25 +0200 (Wed, Jul), Christoph Gysin wrote:
> Zhang Weiwu wrote:
> >zhangweiwu@Bach:/tmp$ diff -I "^[[:space:]]*/[*].*[*]/[[:space:]]*$"
> >header.inc.php empty
> >1,2d0
> >< <?php
> ><       /* $Id: header.inc.php.template,v 1.58 2005/07/08 05:00:14 milosch
> >Exp $ */
> >
> >in man it's being said,
> >       -I RE  --ignore-matching-lines=RE
> >              Ignore changes whose lines all match RE.
> >
> >I read man grep and it seems there are two sets of RE, extended and basic.
> >But it's not mensioned in diff(1) wheather or not diff(1) takes extended
> >or basic RE. I am using Debian so it should be gnu diff.
>
> If it's not mentioned, it possibly uses basic regular expressions.
>
> try:
>
> $ diff -I '/\* \$Id.*\$ \*/' header.inc.php empty
>
> Christoph

Indeed strange. BUT the clue lies in (after many strange results) in
'man grep' where, on my host, it says exactly:

-I regexp
   Ignore changes that just insert or delete lines that match regexp.

Notice the word: 'changes'.
It seems that it means: ignore if WHOLE GROUP of DELETED OR INSERTED
lines matches (every added or deleted line) the provided regexp.

In your case the first line of header.inc.php is included in change-group
but does not matches RE.

Try (to be very simple):
$ diff -I '^.*/.*$' header empty
1,2d0
< <?php
<         /* $Id: header.inc.php.template,v 1.58 2005/07/08 05:00:14 milosch Exp $ */

$ echo '<?php' > empty
$ diff -I '^.*/.*$' header empty
(nothing)
$ :>empty
$ diff -I '^.*php.*$' header empty
(nothing - because BOTH lines, considered CHANGED OR DELETED have the
word 'php' inside)

Now the difficult part: how to solve the real problem. :-)

* You may compare grepped files (with grepped out /* $Id:$ */)
* You may try to filter diff output... but I don't like this (by
  intuition - I may be wrong)
* experiment with various options of diff. If only output (not retcode)
  matters then good candidate maybe may be --changed-group-format, which is
  weel described in 'info diff'
* or something other...

HTH

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