grep
-v: invert the search (show lines without match)
^: beginning of a line
\s: any kind of space
\s*: any amount (0-Inf) of any kind of space
$: end of line
^\s*$: only space between begin and end of a line
^\s*!: only space between beginning of a line, and a "!", denoting beginning of comment.
-E: extended regular expression. Otherwise | has to be replaced by \| if there is no -E