What is the difference between ps -ef | grep WDA and ps -ef | grep [W]DA?

Question

What is the difference between

ps -ef | grep WDA

and

ps -ef | grep [W]DA

How exactly [] rids of the unwanted info?

Usual reminder that `pgrep` can likely replace `ps ... | grep ...` and that `pgrep` is clever enough to not match itself. — thrig, Jul 09 '17 at 13:46

score 3 · Answer 1 · answered Jul 09 '17 at 13:43

WDA is a regular expression that matches itself. Thus the output will sometimes include the process listing for the grep process.

[W]DA is a regular expression that does not match itself. Thus the output will not include the process listing for the grep process.

1 Answers1