How does ps aux | grep '[p]attern' exclude grep itself?

Question

The title says it all. I\'ve seen this idiom used alot instead of adding an additional grep -v grep in some ps pipeline. For example it could be used l

Answer 1

The pattern [f]irefox will not match the literal string [f]irefox. Instead it will match strings with exactly one char from the 1-character class [f], followed by irefox.