[RndTbl] Grep supports Perl regexp! Who knew?

Gilbert E. Detillieux gedetil at cs.umanitoba.ca
Wed Jan 9 12:18:51 CST 2013

On 2013-01-09 12:01, Adam Thompson wrote:
> Command Line Magic (@climagic) tweeted at 11:58 AM on Wed, Jan 09, 2013:
> grep -o -P "(?<=CRON\[)\d+" /var/log/syslog # GNU grep supports perl regex expressions. This gives only the PID on CRON lines in syslog.
> (https://twitter.com/climagic/status/289068621362241537)

Who knew?  I did, and so did the man page...

    -P, --perl-regexp
         Interpret PATTERN as a Perl regular expression.  This is  highly
         experimental and grep -P may warn of unimplemented features.

And whether or not it's "highly experimental" (i.e. likely to blow up, 
or just likely to no be supported in future versions?), it is highly 
non-portable, since it's only GNU grep that supports it.

Actually, I had discovered this extension when researching the grep 
family for an RTFM topic a few years ago...


Gilbert E. Detillieux		E-mail: <gedetil at muug.mb.ca>
Manitoba UNIX User Group	Web:	http://www.muug.mb.ca/
PO Box 130 St-Boniface		Phone:  (204)474-8161
Winnipeg MB CANADA  R2H 3B4	Fax:    (204)474-7609

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