Re: grep -e '\(a\)\1' -e '\(b\)\1'

[Alain Magloire]

> 
> address@hidden (Hans-Bernhard Broeker) writes:
> 
> > Tapani Tarvainen <address@hidden> wrote:
> > 
> > > The grep command in the subject line doesn't work
> > > correctly with Gnu grep 2.4: it fails to match 'bb'.
> > 
> > Looks like pilot error, to me:
> > 
> > $ echo bb | grep -e '\(a\)\1' -e '\(b\)\2'
> > bb
> 
> That's not the way it should work: multiple -e arguments
> should be treated as independent patterns and back references
> should not refer to previous ones.

Agreed.

> At least that's how I read POSIX.2, and that's the way
> HP-UX grep works.
> 
> Same applies when multiple patterns are separated by newline:
> 
> grep '\(a\)\1
> \(b\)\1'
> 
> should match aa and bb, not ba.

Agreed.

> Incidentally,
> 
> echo ba | grep -e '\(a\)\1' -e '\(b\)\1'
> 
> doesn't print anything either.

I think we can agreed that current behaviour of GNU grep for BRE
should be fix. 

> > > Same problem with egrep '(a)\1|(b)\1'.
> > 
> > $ echo bb | egrep '(a)\1|(b)\2'
> > bb
> 
> There you are correct, now they are in the same pattern
> (and that's a nonportable Gnu extension anyway).
> But again,
> 
> echo ba | egrep '(a)\1|(b)\1'   
> 
> doesn't print ba either.

If you are sticking with POSIX.2, For ERE the expression is not
portable since, for example on my Solaris box:

$ echo b1a | /usr/xpg4/bin/egrep '(a)\1|(b)\1'
b1a

Thanks for the feedback.

-- 
au revoir, alain
----
Aussi haut que l'on soit assis, on n'est toujours assis que sur son cul !!!