[script] check for a running process

mikshaw · 01-13-2004, 07:24 PM

I'm wondering if there is a more efficient/compatible way to do this:

Code:

if [ -n "$(ps -A | grep root-tail)" ]; then
   echo "root-tail is already running"
else
   root-tail -f -g 120x30+8+8 ${HOME}/log/console,brown,'messages'
fi

It works for me in a bash script, but I understand $(command) does not work in other shells.
I tried

Code:

if [ -n `ps -A | grep root-tail` ]

but it doesn't seem to work.

Thanks for any help.

lyle_s · 01-13-2004, 08:21 PM

You're using command substitution, which substitutes the standard output of a command. All you're looking for if the return value of the command.

Code:

if ps -C root-tail > /dev/null; then
	echo "root-tail is already running"
else
	root-tail -f -g 120x30+8+8 ${HOME}/log/console,brown,'messages'
fi

Lyle

mikshaw · 01-13-2004, 08:33 PM

Hmmm...that looks interesting.
However, ps -C <command> still returns "PID TTY TIME CMD" even if the specified process isn't running, which is why I added the grep.
So maybe if `ps -A | grep root-tail` > /dev/null; would work?

Oh...it seems the "PID TTY TIME CMD" doesn't have any effect, so it works fine.
Thank you