This and other RFCs are available on the web at
http://dev.perl.org/rfc/
=head1 TITLE
Regular Expression Special Variables
=head1 VERSION
Maintainer: Uri Guttman <[EMAIL PROTECTED]>
Date: 25 Aug 2000
Version: 1
Mailing List: [EMAIL PROTECTED]
Number: 158
=head1 ABSTRACT
This RFC addresses ways to make the regex special variables $`, $& and
$' not be such pariahs like they are now.
=head1 DESCRIPTION
$`, $& and $' are useful variables which are never used by any
experienced Perl hacker since they have well known problems with
efficiency. Since they are globals, any use of them anywhere in your
code forces all regexes to copy their data for potential later
referencing by one of them. I will describe some ideas to make this
issue go away and return these variables back into the toolbox where
they belong.
=head1 IMPLEMENTATION
There are two part I have for the implementation and they work together.
First, $`, $& and $' will be scoped just like $1 and friends. They will
be set by the regex and be only accessible in the current block or a
block which starts with a regex like:
if ( /foo/ ) {
But the problem of knowing whether those vars are used by a given regex
remains. This is solved by a new modifier k (for keep). This tells the
regex to do the copy so the 3 vars will work properly. So you would use
code like this:
$str = 'prefoopost' ;
if ( $str =~ /foo/k ) {
print "pre is [$`]\n" ;
print "match is [$&]\n" ;
print "post is [$']\n" ;
}
print "$` is undefined here.\n" ;
=head1 IMPACT
None
=head1 UNKNOWNS
None
=head1 REFERENCES
None
