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

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 9, 2017 at 13:46

JdeBP · Accepted Answer · 2017-07-09 13:43:52Z

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.

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