I'm confused: the regexp you show should match an empty string. It looks like this: /
^ # from the start
( # match
( [\w\d\-\_]+ ) # one or more of [class]
[:,] # followed by a delimiter
| # or match
# nothing # nothing
) # then
( .* ) # match zero or more characters
$ # .. until we reach end of string
/x
This will match against any string that doesn't have newlines in it, and since undef evaluates to the empty string in a string context, it will match (taking advantage of the "or match ... nothing" option).
I don't have perl5.005_02 here, but I tried this: perl -wle 'print "ok" if undef =~ /^(([\w\d\-\_]+)[:,]|)(.*)$/'
.. against each of 5.004, 5.004_05, 5.005_03 and 5.6.1 and it printed the expected warning and the expected "ok" in each case.
Can you come up with a short example like mine that prints "ok" on one of those perl builds, but not on the other?
Hugo
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