Well "time" essentially does what the other script in this thread
does, in a way.  It just sits in the background until the process
dies, then compares the start and end time. (my guess, that's how I'd
do it)



On 10/26/05, Erik Bixby <erik.bixby@gmail.com> wrote:
> So, I'm guessing there's no elegant way of doing what I want, something
> similar to "time" that calls a command and acts upon it, somehow...
>  -Erik
>
>
> On 10/26/05, vodhner@cox.net <vodhner@cox.net> wrote:
> > Erik wrote:
> > > I was wondering if anyone knew a way to allow a shell
> > > command to run for a specific period of time.  In this
> > > particular case, I want tcpdump to run for 23 hours,
> > > 59 minutes, 59 seconds.
> >
> > It would be best if the process could limit itself, since anything you do
> in a shell script will have sloppy timing, maybe a few seconds off.  But you
> can do this for any process, using the following crude approach within a
> single script:
> >
> > This script should be run with all its output redirected to a log file, so
> you can have a record of how it went.
> >
> > Run your process (tcpdump) in the background with &
> >
> > This becomes an independent process, so the next command in your script
> will start immediately:
> >
> > date  # output goes into your log file.
> >
> > sleep 86399  # Or less, since kill won't be instantaneous
> >
> > date
> >
> > Use a pipeline with "ps -ef" and "grep" to identify the running tcpdump
> process.  Extract the pid using "cut" and do a "kill".
> >
> > sleep 2   # just to give kill time to take effect
> >
> > ps -ef | grep ... # Did it go away?
> >
> > date
> >
> > exit
> >
> > Details on request, but the above commands are good things to learn.  This
> type of ps + grep pipeline is also useful to detect if a duplicate copy of a
> script is running, etc.
> >
> > The sleep command is only precise to within a second or two, and other
> system activity might delay the next command.
> >
> > Vic
> >
> >
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