topic Re: trap process id in Operating System - HP-UX

trap process id

Dominic Ouellet — Wed, 01 Aug 2001 16:34:30 GMT

I everybody,

Here is the situation. I need to recover the PID of a program I launched in background (from a script). Other scripts may have launched the same program so a simple ps | grep command wouldn't do the job. I feel unsure with the $! command (witch return the PID of the last background program that has been launched) because two script could launch background programs at the same time and then, I can't be sure I got the PID of my program. I also heard about the ps -H but it only applies for XPG4. Any ideas?

Thanks for your help...
Dom

Re: trap process id

Dan Bonham — Wed, 01 Aug 2001 16:53:45 GMT

Dom,
I think the $! is the best way to go. You should be ok because $! is local to the shell you are in so it should not know the PID of a background process started in another shell.

Rusty

Re: trap process id

James R. Ferguson — Wed, 01 Aug 2001 16:55:36 GMT

Hi:

While pid values will eventually be reused (when they are no longer in use), there is no problem with capturing a pid in a variable and later referencing/testing it.

See this recent thread for some examples:

http://forums.itrc.hp.com/cm/QuestionAnswer/1,1150,0xfe7387dc4d7dd5118ff00090279cd0f9,00.html

ALSO: if you want to leverage the UNIX95 options of 'ps' all you need do is arm the UNIX95 variable for the duration of the 'ps' like this (your offering):

UNIX95= ps -H

Note the blank character after the equal sign and the absence of any semicolon! This syntax sets UNIX95 only for the command on the line it is written.

...JRF...

Re: trap process id

A. Clay Stephenson — Wed, 01 Aug 2001 17:02:24 GMT

Hi,

It doesn't matter if another process also spawns a process of the same name. $! will definitely be the pid of the last background child process spawned by this shell.

Clay

Re: trap process id

Dominic Ouellet — Wed, 01 Aug 2001 17:37:32 GMT

Thanks to both of you guys
I'm now a happy camper :-)