The regular expression captured submatches ($1, $2, ...) are now more consistently unset if the match fails, instead of leaving false data lying around in them.
I believe this is referring to the fact that if a match has $1..$6 in one successful match, then only $1..$2 in the next match, that $3..$6 are more carefully set to undef now. I remember there being a patch to that effect.

If they were to change the other behavior, it would no longer be (usefully) upward compatible. This would have been a grave mistake, caught by someone (like me).

The reason the variables are not unset on failure is to permit: 

if ($string = /... ( ... ) .../) { # overall match
  if ($1 =~ /foo/) { # and $1 contains foo
  ...
  } elsif ($1 =~ /bar/) { # nope?  how about bar
  ...
  }
}

[download]
If $1 reset on the failed match on the second line, then we couldn't do the third match. This has been by design in Perl for over a decade now. (And I just verified that 5.8.5 doesn't unset the variables, so it works as it always has.)

-- Randal L. Schwartz, Perl hacker
Be sure to read my standard disclaimer if this is a reply.

In reply to •Re^3: You *Can* Catch errors in closing lexical filehandles by merlyn
in thread Catching errors in closing lexical filehandles by gaal

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