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From: stan@amc.UUCP (Stan Tazuma)
Newsgroups: net.sources
Subject: Re: csh-script to run a job after an existing job terminates
Message-ID: <212@amc.UUCP>
Date: Thu, 24-Jul-86 19:30:03 EDT
Article-I.D.: amc.212
Posted: Thu Jul 24 19:30:03 1986
Date-Received: Fri, 25-Jul-86 21:41:49 EDT
References: <515@cubsvax.UUCP>
Reply-To: stan@amc.UUCP (Stan Tazuma)
Organization: Applied Microsystems Corp.; Redmond, Wa.
Lines: 95

In article <515@cubsvax.UUCP> peters@cubsvax.UUCP (Peter S. Shenkin) writes:
>
>DESCRIPTION:
>after:	a procedure that waits until a particular running process terminates, 
>	then initiates a new process.  This runs under csh, but should be
>	easily translatable to bsh or ksh.
>
I think it's a useful tool, but there are simpler ways to do it (at
least under a BSD Unix (which includes the Ultrix you're using)).
Here's a program I came up with a while back.  It's called waitp.
It has the same args. as "after".
------------waitp.c------------
/* this program will wait until a given process dies
 *  e.g.   waitp  10309  10
 *
 * 3/12/85 - skt
 */
#include <stdio.h>

#define DEFAULT_PAUSE		30

extern errno;

main(argc,argv)
int argc;
char **argv;
{
    char *cmdname = argv[0];
    int pid;
    register ret;
    register sleep_time = (argc > 2) ? atoi(argv[2]) : DEFAULT_PAUSE ;

    if (argc == 1) {
	fprintf(stderr, "usage:  %s  pid  [ pause-time ]\n", cmdname);
	exit(1);
    }
    pid = atoi(argv[1]);
    while ((ret = getpgrp(pid)) >= 0)
	if (sleep_time > 0) sleep(sleep_time);

    /* getpgrp returns -1 when the process goes away, and
     * sets errno == 3 (ESRCH in /usr/include/errno.h)
     */
    /* printf("getpgrp returned %d\n", ret); */
    /* printf("errno is %d\n", errno); */

    exit(0);
}
-----------------
The way to use this is as follows.  Suppose you start a job in the
background.  Then you want to run another job after that one completes.
First do a "jobs" to find out the pid of the first job; let's suppose
the pid is 12345.  Then run the job:

	waitp 12345; <arbitrary command> &

--------------
If you want to do it as a shell script, the ps command can be used
to look at an arbitrary process, by pid.  E.g.,
--------------(first, in csh since your script was in csh)
#! /bin/csh -f
set pid = $1
if ($#argv == 2) then
    set sleep_time = $2
else
    set sleep_time = 30
endif
while (1)
    if ( { ps \#$pid } ) then >/dev/null
	sleep $sleep_time
    else
	exit 0
    endif
end
--------------(here, in sh since sh probably has less impact on the system)
#! /bin/sh
pid=$1
sleep_time=${2-30}
while :
do
    if ps \#$pid >/dev/null
    then
	sleep $sleep_time
    else
	exit 0
    fi
done
---------------
For AT&T Unix versions, getpgrp() doesn't behave in the above way (waitp.c).
The AT&T ps command can be used to look at a specific process, though
using a different ps argument than above.

Stan Tazuma
Applied Microsystems Corp.
	...uw-beaver!tikal!amc!stan