Using ! operator on a shell command -

i'm trying write script if particular string not present in file.

i know in order check if string available, can like:

if grep -qi "sms" $file; 

but how combine ! operator shell command?

just add in front of condition make evaluate on contrary:

if ! grep -qi "sms" $file; echo "yes"; fi    ^ 

test

$ cat hello bye $ if ! grep -qi "sms" a; echo "sms not found"; fi sms not found