in reply to Regex bug? matching multiple newline with /m

$ is a zero-width match, it does not consume a \n; 

[rick@ry ~]$ perl -e 'use strict; printf "%s\n", "ab\nab\n" =~ /^ab$ab
+$/m'
Global symbol "$ab" requires explicit package name (did you forget to 
+declare "my $ab"?) at -e line 1.
Execution of -e aborted due to compilation errors.
[rick@ry ~]$

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Try adding the 'use strict;' to your other examples to see what they are really doing.

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Re^2: Regex bug? matching multiple newline with /m
by NERDVANA (Priest) on Aug 09, 2021 at 10:41 UTC
    Ha, yes bitten by interpolation. Thanks.

    Now I'm wondering how many times in the past I've had difficulties with a multiline regex and it was due to the incorrect assumption that it would consume the \n...

[reply]
      ... bitten by interpolation.

      Perhaps better to say "bitten by failure to enable strict" (and I would also recommend warnings).

      Give a man a fish:  <%-{-{-{-<

[reply]
[d/l]
      The problem with interpolation is covered in the documentation for  /PATTERN/msixpodualngc in Regexp Quote Like Operators.
      If "'" is used as the delimiter, no variable interpolation is done.

      This is not enough to solve your problem with the newline because $ is a zero width assertion. Assertions

      Besides "^" and "$", Perl defines the following zero-width assertions:

      In this case, it is probably best to match the newline explicitly and not use the anchor at all.

      Bill
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