Grep

• Show all lines that do not contain blabla

grep -v blabla filename.txt

• Match any character

With a dot (.) you can match any character

grep -E "L.nux"

Matches Linux, Lanux L nux, but not Lnux

• Match all characters

With a .* you can match an arbitrary count of any character

grep -E "L.*nux"

Matches Linux, Liinux, Lanux, L nux and Lnux

• Match any character but blank

grep -E "L[^ ]nux"

Match Linux, Lanux, but not Lnux and not L nux

See also

• regex