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

i want write in bash script piece of code checks if program running. have following in order search whether bar running

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

the

 grep -v grep 

part ensure "grep bar" not taken account in ps results

when bar isn't running, foo correctly empty. problem lies in fact tha script has

 set -e 

which flag terminate script if command returns error. turns out when bar isn't running, "grep -v grep" doesn't match , grep returns error. tried using -q or -s no avail.

is there solution that? thx

sure:

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

or even:

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