topic Re: regexp vs. GNU regexp in Operating System - Linux

regexp vs. GNU regexp

Dusan Onofer — Mon, 24 Apr 2006 06:33:57 GMT

Hi,

i'm trying to get one script working with hp-ux's grep (porting from GNU's grep) and i've found different behavior. I'm asking here if someone could explain it:

Text (from comma separated values) which is GNU's grep (in Cygwin) selecting (according to my opinion) correctly and (extened) regular expresion is like this:
^X:([^,]*,){3}"C

i'm testing it (fourth comma separated value is like "C):
$ echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,){3}"C'
X: A,,B,"C",,"D"

ok, match

$ echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,){4}"C'

ok, it doesn't match

But with hp-ux's grep:
$ echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,){3}"C'
X: A,,B,"C",,"D"

match, ok.

$ echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,){4}"C'
X: A,,B,"C",,"D"

why this match?

echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,){5}"C'
X: A,,B,"C",,"D"

also match. Why?

$ uname -a
HP-UX ccbdevd1 B.11.11 U 9000/800 610389312 unlimited-user license

thanks a lot!

Dusan

Re: regexp vs. GNU regexp

harry d brown jr — Mon, 24 Apr 2006 08:28:10 GMT

Dusan,

It does appear to be a bug :-(

manually expanded it works:

[root@vpart1 /]# echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,){5}"C'
X: A,,B,"C",,"D"
[root@vpart1 /]# echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,)([^,]*,)([^,]*,)([^,]*,)([^,]*,)"C'
[root@vpart1 /]# echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,)([^,]*,)([^,]*,)([^,]*,)([^,]*,)"C'
[root@vpart1 /]# echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,)([^,]*,)([^,]*,)([^,]*,)"C'
[root@vpart1 /]# echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,)([^,]*,)([^,]*,)"C'
X: A,,B,"C",,"D"
[root@vpart1 /]# echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,)([^,]*,)"C'
[root@vpart1 /]# echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,)"C'
[root@vpart1 /]# echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,){2}"C'
[root@vpart1 /]# echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,){3}"C'
X: A,,B,"C",,"D"
[root@vpart1 /]# echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,){4}"C'
X: A,,B,"C",,"D"
[root@vpart1 /]# echo 'X: A,,B,"C",,"D"'|grep -E '^X:([^,]*,){6}"C'
[root@vpart1 /]#

Even with regexbuilder (http://sourceforge.net/project/showfiles.php?group_id=76775) any variation other than
^X:([^,]*,){3}"C
is invalid

Report it as a bug.

I personally would use 'cut -d"," -f4' with grep "\"C\"", but that's not really the reported problem.

live free or die
harry d brown jr

Re: regexp vs. GNU regexp

Dusan Onofer — Mon, 24 Apr 2006 09:47:09 GMT

Harry,

thanks for your reply.

It seems to me, it's in libc or where -- sed's behaviour is same.

$ echo 'X: A,,B,"C",,"D"'|sed 's/^X:$[^,]*,$\{2\}"C/deleted/'
X: A,,B,"C",,"D"
$ echo 'X: A,,B,"C",,"D"'|sed 's/^X:$[^,]*,$\{3\}"C/deleted/'
deleted",,"D"
$ echo 'X: A,,B,"C",,"D"'|sed 's/^X:$[^,]*,$\{4\}"C/deleted/'
deleted",,"D"
$ echo 'X: A,,B,"C",,"D"'|sed 's/^X:$[^,]*,$\{5\}"C/deleted/'
deleted",,"D"

also attached program reports false match.

btw, where can I report a bug?
(sorry, I've tryied "googling" over hp.com but didn't find
any useful links).

Re: regexp vs. GNU regexp

Dusan Onofer — Mon, 24 Apr 2006 09:53:45 GMT

compilable version.

Dusan

Re: regexp vs. GNU regexp

harry d brown jr — Tue, 25 Apr 2006 08:41:26 GMT

You might find this tool very useful:

http://www.weitz.de/regex-coach/#install

This proves to be the best pattern:

^(X: )([^,]*,)([^,]*,)([^,]*,)(\"C\"\,)([^,]*,)([^,]*)

Using a ([^,]*,){3} instead of manually repeating it causes the pattern to backtrace and grab the same pattern twice. Try your different variations and use the STEP tab (near bottom of window) to walk through the string.

live free or die
harry d brown jr

Re: regexp vs. GNU regexp

Marlou Everson — Tue, 25 Apr 2006 14:37:30 GMT

Dusan,

You can report bugs through "Support Case Manager" under the "Maintenance and support for hp products" link.

Marlou