I think that it does set undef for non-captured delimiters in a split regex that contains capturing parens. Look at this example: 

my $string = qq/This&and+that/;
my @segments = split /(&)|\+/, $string;
print "$_\n" foreach @segments;

__OUTPUT__
This
&
and
Use of uninitialized value in (.) concatenation or string at mytest.pl
+ line 4.

that

[download]

In that example, you can see that the non-capturing portion of the match results in undef being plopped into the list element pertaining to that portion of the split.

As for documentation, the POD for split says, "If the PATTERN contains parentheses, additional list elements are created from each matching substring in the delimiter."

This is correct. It appears to be true that additional elements are created for each matching substring in the delimiter if the PATTERN contains parenthesis. But what it doesn't tell you is that though elements are created for each matching substring, those elements are only populated with a value if the corresponding portion of the PATTERN also uses capturing parens. If the specific portion of PATTERN that matched isn't captured with parens, the element is still created (since parens were used somewhere else within PATTERN), but the element isn't populated.

In this case, I would consider this a bug, either in the documentation (for not documenting what happens if you combine both capturing and noncapturing components in the split PATTERN), or a bug in Perl's split, for not quite accomplishing DWIMery.


Dave

In reply to Re^4: split and capture some of the separators by davido
in thread split and capture some of the separators by shemp

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