Quote

If the PATTERN evaluates to the empty string, the last success-
fully matched regular expression is used instead. In this case,
only the "g" and "c" flags on the empty pattern is honoured - the
other flags are taken from the original pattern. If no match has
previously succeeded, this will (silently) act instead as a gen-
uine empty pattern (which will always match). perlop#Regexp_Quote_Like_Operators

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$\="\n";
print "b" =~ //;        #1
print "a" =~ /a/;       #1
print "a" =~ /b/;
print "b" =~ //;
print "a" =~ //;        #1

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man vergleiche Zeile 2 und 5!

moritz+2008-07-25 08:47:16--

Was war denn die vor Zeile 2 zuletzt gematchte Regex?
Wenn du das nicht weisst ist es auch nicht sinnvoll gegen // zu matchen.

Quote

If no match has previously succeeded, this will (silently) act instead as a gen-
uine empty pattern (which will always match).

renee+2008-07-25 07:52:12--

Zum Thema "emtpy pattern" gab es letzt bei den Perl 5 Porters eine Diskussion:

http://perl.markmail.org/search/?q=empty+pattern+d...

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if (m/$pat1/ or m/$pat2/ or m/$pat3/) {
   s///;
}