Using ! operator on a shell command

Question

I'm trying to write a script which does something if a particular string is not present in a file.

I know that in order to check if string is available, we can do something like:

if grep -qi "sms" $FILE; then

But how do I combine a ! operator with a shell command?

Answer 1

Just add it in front of your condition to make it evaluate on the contrary:

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

Test

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