$nothing = 1;
}
+or, using experimental C<EVAL blocks> of regular expressions
+(see L<perlre/"(?{ code })">),
+
+ / ^abc (?{ $abc = 1 })
+ |
+ ^def (?{ $def = 1 })
+ |
+ ^xyz (?{ $xyz = 1 })
+ |
+ (?{ $nothing = 1 })
+ /x;
+
or even, horrors,
if (/^abc/)