Lets dissect this into smaller problems.
I tried to simplify the case to avoid misunderstandings
DB<32> p "hello" =~ s/o*$/O/gr;
DB<33> $_="hello"; s/o*$/O/g; print # for older Perls
Surprise: the o is replaced twice.
Explanation so far
You and Hauke already explained that
- pos isn't changing after the first match b/c of the zero-width of $
- the empty o* is matching again °
(And I agree that the referenced perlre#Repeated-Patterns-Matching-a-Zero-length-Substring needs a rewrite)
DB<41> $_="hello"; say pos,"($1)" while m/(o*$)/g; # pos doesn't c
DB<42> p "hello" =~ s/x*$/O/gr; # empty match (
Now, why is it surprising?
I think your case is that $ in combination with the /m modifier should act differently. Correct?
- Would this be consistent?
- Are there already examples of zero-width assertions who does it that way?
- Are there work-arounds to achieve what you want? (i.e. skipping zero-length matches)
Here a guess for the last question
DB<44> p "hello\nfoo" =~ s/o*\n/O/gmr;
DB<45> p "hello\nfoo\n" =~ s/o*\n/O/gmr; # added \n at the end of
Question @all: Is the problem better understood now? :)
added more code
added headlines for structuring
°) because empty patterns are always matching
DB<59> p "12345" =~ s/x*/ /gmr;
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