siffland has asked for the wisdom of the Perl Monks concerning the following question:

I need some help with pcre grep, I am unsure if it is OK to post for help here, so please tell me if it is not.

Here is what i am trying to accomplish. I need to grep anything out of the /etc/passwd with a UID of 205 or greater and that does not start with a - . The software we are using, cfengine, requires the use of a pcre. So far i have:

pcregrep -v ".*:.*:(-|1)?[0-9]{1,2}:.*:.*:.*" /etc/passwd

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But that yields anything above 200, any help would be appreciated.

If anyone know any great webpages for pcre grep I would love to be pointed that direction. I am not that great with perl regular expressions, but would like to learn more.

Thanks,

Sean

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Re: pcre grep
by duelafn (Parson) on Jun 10, 2010 at 14:42 UTC

    Well, perl can do this easily enough:

    perl -naF: -e 'print if $F[2] >= 205' /etc/passwd

    See documentation for -a in perlrun

    Good Day,
        Dean

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Re: pcre grep
by linuxer (Curate) on Jun 10, 2010 at 20:43 UTC

    I think, you could have a look at the official perldoc to get information about Perl's regular expressions:

    perlretut - Tutorial

    perlrequick - Quick Reference

    perlre - Regex documentation

    And not to forget the pcre man pages:

    http://www.pcre.org/pcre.txt

    If you want/have to stick to pcregrep, I suggest something like: 

    pcregrep -v  "^[^:]*:[^:]*:-?(1?\d?\d|20[0-4]):" /etc/passwd

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    It (simplified) assumes/uses:

    • the pattern is anchored at beginning of line (^)
    • "login name" field must not contain a colon
    • "password" field must not contain a colon
    • "UID" field:
      • leading optional "-"
      • grouped alternatives:
        • number between 0 and 199 OR
        • number between 200 and 204
    • don't care about the rest of the line
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