«,» matches a comma, then «.+?» matches the least possible, then it matches the end of the string or a LF at the end of the string. 

01234567 position
A, B, C

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Full:

  1. Start matching at position 0.
    1. At position 0, «,» doesn't match. ⇒ Backtrack.
  2. Start matching at position 1.
    1. At position 1, «,» matches 1 character.
      1. At position 2, «.+?» matches 1 characters.
        1. At position 3, «$» doesn't match. ⇒ Backtrack.
      2. At position 2, «.+?» matches 2 characters.
        1. At position 4, «$» doesn't match. ⇒ Backtrack.
      3. At position 2, «.+?» matches 3 characters.
        1. At position 5, «$» doesn't match. ⇒ Backtrack.
      4. At position 2, «.+?» matches 4 characters.
        1. At position 6, «$» doesn't match. ⇒ Backtrack.
      5. At position 2, «.+?» matches 5 characters.
        1. At position 7, «$» matches 0 characters. ⇒ Success.

Summary:

  1. Starts matching at position 1.
  2. At position 1, «,» matches 1 character.
  3. At position 2, «.+?» matches 5 characters.
  4. At position 7, «$» matches 0 characters.

If «.+?» were to match any less, the «$» wouldn't match.

Solution: 

sub join_list {
   return "none" if !@_;  # ???
   my $last = pop;
   return $last if !@_;
   return join( ", ", @_ ) . " and " . $last;
}

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In reply to Re: Non-greedy substitution by ikegami
in thread Non-greedy substitution by Bod

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