grep replacement

[Jim Hutchison]

4537 at vdsvax.steinmetz.ge.com, barnett at vdsvax.steinmetz.ge.com (Bruce G. Barnett)
>In <1036 at cfa.cfa.harvard.EDU> wyatt at 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
>
[...]
>
>Have you ever waited for a computer?  

No, never. :-)

>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.
I would agree that it is a bad thing to rely on the granularity of
a pipe.  Here is a sample program which can be used to show you what
I mean.

Name it grep, and use it thus wise:

% ./grep pattern * | head -1

/* ------------- Cut here --------------- */
#include <stdio.h>
#include <signal.h>

sighandler(sig)
    int sig;
{
    if (sig == SIGPIPE)
	fprintf(stderr,"Died from a SIGPIPE\n");
    else
	fprintf(stderr,"Died from signal #%d\n", sig);
    exit(0);
}

main()
{
    signal(SIGPIPE,sighandler);
    for (;;)
	printf("pattern\n");
}
/*    Jim Hutchison   		UUCP:	{dcdwest,ucbvax}!cs!net1!hutch
		    		ARPA:	Hutch at net1.ucsd.edu
Disclaimer:  The cat agreed that it would be o.k. to say these things.  */