Hi, I ran across a strange behavior and I'm wondering if it is a bug, or some obscure documented behavior I should keep in mind.

These match: 

# (not using 'say' because I wanted to try it on old perl versions)
perl -e 'printf "%s\n", "ab\nab\n" =~ /^ab$ab$/m'
perl -e 'printf "%s\n", "ab\nab\n" =~ /^(ab$ab$)/m'
perl -e 'printf "%s\n", "ab\nab\n" =~ /^(ab$ab)$/m'
perl -e 'printf "%s\n", "ab\nab\n" =~ /^(ab)$ab$/m'
perl -e 'printf "%s\n", "ab\nab\n" =~ /^(a)b$ab$/m'

[download]

(with '$' consuming a "\n" because it is /m mode)

These do not match: 

perl -e 'printf "%s\n", "ab\nab\n" =~ /^(ab$a)b$/m'
perl -e 'printf "%s\n", "ab\nab\n" =~ /^(ab$)ab$/m'
perl -e 'printf "%s\n", "ab\nab\n" =~ /^ab$(ab)$/m'
perl -e 'printf "%s\n", "ab\nab\n" =~ /^(ab$){2}/m'
perl -e 'printf "%s\n", "ab\nab\n" =~ /(ab$){2}/m'
perl -e 'printf "%s\n", "ab\nab\n" =~ /(?^:^(?^m:(ab$){2}))/m'

[download]

This is greedy but only matches one line 

perl -e 'printf "%s\n", "ab\nab\n" =~ /^((?:ab$)+)/m'

[download]

and it seems to me that all of them should match. This appears to happen as old as 5.8.9 and as new as 5.32.1

Any insights?

In reply to Regex bug? matching multiple newline with /m by NERDVANA

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