"qr//" interpolation¶

This policy can be confused by interpolation of "qr//" elements, but those are always false negatives. For example:

    my $foo_re = qr/(foo)/;
    my ($foo) = m/$foo_re (bar)/x;

A human can tell that this should be a violation because there are two captures but only the first capture is used, not the second. The policy only notices that there is one capture in the regexp and remains happy.

"@-", "@+", $LAST_MATCH_START and $LAST_MATCH_END¶

This policy will only recognize capture groups referred to by these variables if the use is subscripted by a literal integer.

$^N and $LAST_SUBMATCH_RESULT¶

This policy will not recognize capture groups referred to only by these variables, because there is in general no way by static analysis to determine which capture group is referred to. For example,

    m/ (?: (A[[:alpha:]]+) | (N\d+) ) (?{$foo=$^N}) /smx

makes use of the first capture group if it matches, or the second capture group if the first does not match but the second does.

split()¶

Normally, this policy thinks that if a capture is used at all it must be used before the next regular expression in the same scope. The regular expression in a "split()" needs to be exempted because it does not affect the caller's capture variables.

At present, this policy recognizes and exempts the regular expressions in

    split /.../, ...

and

    split( /.../, ... )

but more exotic syntax may produce false positives.