$ grep hello $ grep hello world grep: world: No such file or directory $ grep 'hello world' $ grep . $ grep [0123456789] $ grep [0-9] $ grep [5-9] $ grep [9-5] $ grep [9-9] $ grep [.] $ grep [aeiou] $ grep h[ae]llo $ grep h[^ae]llo $ grep h[0-9a-z]llo $ grep h[^0-9a-z]llo $ grep [:punct:] $ grep [[:alpha:]] $ grep [[:upper:]] $ grep [[:punct:]] $ grep [[:space:]] $ grep '\w'