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Re: grep: show matching line from pattern file

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On 3/06/22 07:17, Greg Wooledge wrote:
> On Thu, Jun 02, 2022 at 03:12:23PM -0400, duh wrote:
> 
>> > > Jim Popovitch wrote on 28/05/2022 21:40:
>> > > > I have a file of regex patterns and I use grep like so:
>> > > > 
>> > > >      ~$ grep -f patterns.txt /var/log/syslog
>> > > > 
>> > > > What I'd like to get is a listing of all lines, specifically the line
>> > > > numbers of the regexps in patterns.txt, that match entries in
>> > > > /var/log/syslog.   Is there a way to do this?
> 
>> $cat -n /var/log/syslog | grep warn
>> 
>> and it found "warn" in the syslog file and provided line numbers. I have
>> not used the -f option
> 
> You're getting the line numbers from the log file.  The OP wanted the line
> numbers of the patterns in the -f pattern file.
> 
> Why?  I have no idea.  There is no standard option to do this, because
> it's not a common requirement.  That's why I wrote one from scratch
> in perl.
> 

I don't know what the OP's use case is, but here's an example I might use:

I have a bunch of custom ignore files for logcheck. After a software 
upgrade, I might want to check which patterns no longer match anything, 
and can be deleted or modified.

I'd really still want to check with real egrep, though, rather than 
using perl's re engine instead.

Cheers,
Richard

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grep: show matching line from pattern file Jim Popovitch <jim@k4vqc.com> - 2022-05-28 22:00 +0200
  Re: grep: show matching line from pattern file The Wanderer <wanderer@fastmail.fm> - 2022-05-28 22:10 +0200
    Re: grep: show matching line from pattern file Greg Wooledge <greg@wooledge.org> - 2022-05-28 23:20 +0200
      Re: grep: show matching line from pattern file The Wanderer <wanderer@fastmail.fm> - 2022-05-28 23:30 +0200
      Re: grep: show matching line from pattern file Jim Popovitch <jim@k4vqc.com> - 2022-05-29 19:50 +0200
      Re: grep: show matching line from pattern file Will Mengarini <seldon@eskimo.com> - 2022-06-03 00:30 +0200
        Re: grep: show matching line from pattern file David Christensen <dpchrist@holgerdanske.com> - 2022-06-03 01:00 +0200
          Re: grep: show matching line from pattern file Will Mengarini <seldon@eskimo.com> - 2022-06-03 02:20 +0200
  Re: grep: show matching line from pattern file Jörg-Volker Peetz <jvpeetz@web.de> - 2022-05-29 15:10 +0200
    Re: grep: show matching line from pattern file David Wright <deblis@lionunicorn.co.uk> - 2022-05-29 15:50 +0200
      Re: grep: show matching line from pattern file duh <fill_in_the_blanks@email.com> - 2022-06-02 21:20 +0200
        Re: grep: show matching line from pattern file Greg Wooledge <greg@wooledge.org> - 2022-06-02 21:20 +0200
          Re: grep: show matching line from pattern file Richard Hector <richard@walnut.gen.nz> - 2022-06-04 05:00 +0200

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