Xref: utzoo comp.unix.wizards:9348 comp.unix.questions:7584
Path: utzoo!attcan!uunet!husc6!mailrus!tut.cis.ohio-state.edu!mandrill!hal!ncoast!allbery
From: allbery@ncoast.UUCP (Brandon S. Allbery)
Newsgroups: comp.unix.wizards,comp.unix.questions
Subject: Re: grep replacement
Message-ID: <7973@ncoast.UUCP>
Date: 13 Jun 88 21:51:49 GMT
References: <7882@alice.UUCP> <5630@umn-cs.cs.umn.edu> <6866@elroy.Jpl.Nasa.Gov> <4524@vdsvax.steinmetz.ge.com> <1036@cfa.cfa.harvard.EDU> <4537@vdsvax.steinmetz.ge.com> <5007@sdcsvax.UCSD.EDU>
Reply-To: allbery@ncoast.UUCP (Brandon S. Allbery)
Followup-To: comp.unix.wizards
Organization: Cleveland Public Access UN*X, Cleveland, Oh
Lines: 33

As quoted from <5007@sdcsvax.UCSD.EDU> by hutch@net1.ucsd.edu (Jim Hutchison):
+---------------
| 4537@vdsvax.steinmetz.ge.com, barnett@vdsvax.steinmetz.ge.com (Bruce G. Barnett)
| >In <1036@cfa.cfa.harvard.EDU> wyatt@cfa.harvard.EDU (Bill Wyatt) writes:
| >|> There have been times when I wanted a grep that would print out the
| >|> first occurrence and then stop.
| >|
| >|grep '(your_pattern_here)' | head -1
| >
| >There are times when I want the first occurrence of a pattern without
| >reading the entire (i.e. HUGE) file.
| 
| I realize this is dependent on the way in which processes sharing a
| pipe act, but this is a point worth considering before we get yet
| another annoying burst of "cat -v" type programs.
| 
| grep pattern file1 ... fileN | head -1
| 
| This should send grep a SIGPIPE as soon as the first line of output
| trickles through the pipe.  This would result in relatively little
| of the file actually being read under most Unix implementations.
+---------------

Not true.  The SIGPIPE is sent when "grep" writes the second line, *not*
when "head" exits!  If there *is* only one line containing the pattern, grep
will happily read all of the (possibly large) files without getting SIGPIPE.
This is not pleasant, even if it's only one large file -- say a
comp.sources.unix posting which you're grepping for a Subject: line.
-- 
Brandon S. Allbery			  | "Given its constituency, the only
uunet!marque,sun!mandrill}!ncoast!allbery | thing I expect to be "open" about
Delphi: ALLBERY	       MCI Mail: BALLBERY | [the Open Software Foundation] is
comp.sources.misc: ncoast!sources-misc    | its mouth."  --John Gilmore