Didn't you rather want to use + instead of * ? 
  DB<48> p "hello\nfoo" =~ s/o*$/O/gmr;
hellOO
fOO
  DB<49> p "hello\nfoo" =~ s/o+$/O/gmr;
hellO
fO
  DB<50>

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Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery

In reply to Re: You won't believe what this regular expression does! by LanX
in thread You won't believe what this regular expression does! by salva

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