bash - Prevent grep returning an error when input doesn't match

Question

I want to write in a bash script a piece of code that checks if a program is already running. I have the following in order to search whether bar is running

 foo=`ps -ef | grep bar | grep -v grep`

The

 grep -v grep

part is to ensure that the "grep bar" is not taken into account in ps results

When bar isn't running, foo is correctly empty. But my problem lies in the fact tha the script has

 set -e

which is a flag to terminate the script if some command returns an error. It turns out that when bar isn't running, "grep -v grep" doesn't match with anything and grep returns an error. I tried using -q or -s but to no avail.

Is there any solution to that? Thx

Answer 1

Sure:

ps -ef | grep bar | { grep -v grep || true; }

Or even:

ps -ef | grep bar | grep -v grep | cat