c:\@Work\Perl>perl -wMstrict -MO=Deparse,-p -le
"! $_ =~ /;\s+/;
"
BEGIN { $^W = 1; }
BEGIN { $/ = "\n"; $\ = "\n"; }
use strict 'refs';
((!$_) =~ /;\s+/);
-e syntax OK

##</code><code>##

! ($_ =~ /;\s+/);
# or
$_ !~ /;\s+/;