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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