This is a useful feature to have when writing one liners e.g.

    % cat words
    all
    these
    worlds
    are
    yours
    

Which I believe is one of the reasons Perl allows it:

    % perl -ne 'print unless /^a/' words
    these
    worlds
    yours

And Ruby does too:

    % ruby -ne 'print unless /^a/' words
    these
    worlds
    yours