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Starting in Perl 5.14, a "^" (caret or circumflex accent) immediately after the "?" is a shorthand equivalent to "d-imsx".
Flags (except "d") may follow the caret to override it. But a minus sign is not legal with it.

Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live. -- Damian Conway in "Perl Best Practices"
lesen: Wie frage ich & perlintro brian's Leitfaden für jedes Perl-Problem