c:\@Work\Perl>perl -wMstrict -le "my @t = qw( regex regex.1 regex.12 regex.1a regex.a regex.abc regex.a1 oregex.2 ); for (@t) { printf qq{'$_'}; printf ' matches!' if /^regex(?!\.[^\d])/; print ''; } " 'regex' matches! 'regex.1' matches! 'regex.12' matches! 'regex.1a' matches! 'regex.a' 'regex.abc' 'regex.a1' 'oregex.2'