Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!jpl-devvax!lwall
From: lwall@jpl-devvax.jpl.nasa.gov (Larry Wall)
Newsgroups: comp.editors
Subject: Re: Multiple line regexps
Keywords: regexp, multiple lines
Message-ID: <1991Jun6.193933.20110@jpl-devvax.jpl.nasa.gov>
Date: 6 Jun 91 19:39:33 GMT
References: <1991Jun2.231351.10229@trl.oz.au> <1991Jun03.045458.4972@convex.com> <2732@root44.co.uk>
Reply-To: lwall@netlabs.com (Larry Wall)
Distribution: comp
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 65

In article <2732@root44.co.uk> gwc@root.co.uk (Geoff Clare) writes:
: Distribution: comp
: Organization: UniSoft Ltd., London, England
: Lines: 18
: 
: tchrist@convex.COM (Tom Christiansen) writes:
: 
: >    perl -00 -ne 'print /(.*\n)/' some_file
: 
: >The -00 put us in paragraph mode, and the (.*\n) isolates the first
: >line of each paragraph for printing.
: 
: The exact equivalent in awk is:
: 
:     awk 'BEGIN { RS=""; FS="\n" }
: 	 { print $1 }' some_file
:     
: The RS="" makes blank lines the record separator, and the FS="\n" allows
: the first line of the record to be obtained using "$1".

That's an exact equivalent except in one Important Respect:

    $ perl -00 -ne 'print /(.*\n)/' u.usa.va.3
    # u.usa.va.3 uucp-map@acsu.buffalo.edu
    #N      ukelele
    #N      un1
    #N      usancon
    #N      usaos
    #N      .uu.net, uunet
    #N      .uucom.com, uucom
    #N      vast
    #N      .verdix.com, vrdxhq
    #N      viar
    #N      virgil
    #N      .virginia.edu, virginia
    #N      virtech
    #N      visenix
    #N      visix
    #N      viusys
    #N      vssadm
    #N      vtserf
    #N      wimpy
    #N      wperkins
    #N      .wsrcc.com, wsrcc.com, wsrcc
    #N      wyvern
    #N      xlisa
    #N      xrxedds
    #N      yendor
    #END u.usa.va.3
    $ awk 'BEGIN { RS=""; FS="\n" }{ print $1 }' u.usa.va.3
    # u.usa.va.3 uucp-map@acsu.buffalo.edu
    #N      ukelele
    #N      un1
    #N      usancon
    #N      usaos
    Segmentation fault (core dumped)

That's on a Vax.  On Suns, at least it's polite enough to give an error
message about the line being too long.

Arbitrary limits are for the birds.  They crap on you when you're already
halfway to the celebration.

Larry Wall
lwall@netlabs.com