$& discussion

Doug Miles doug.miles at
Thu Aug 24 11:56:39 CDT 2000

Michael Dearman wrote:
> Hi guys,
> Enjoyed the get together and meeting you'all.
> Doug Miles wrote:
> >
> > I looked into the $& problem in O'reilly's "Mastering Regular
> > Expressions",
> For Perl ver. 5.003, don't have a clue if this still holds. The author
> has maintained an excellent support site, but I don't remember seeing
> anything addressing this issue.
> >               and found that the inefficiency is caused by perl making a
> > copy of the string that is being matched against.  This is also caused
> > by using '()'s in a regex (which I am doing), so avoiding the use of $&
> Just to round the culprits out - this also happens when $' and $` are used.
> As I read it, this group and parens also disable some optimizations done for
> substitutions. But for parens,this only affects the regex actually in the parens.
> and the /i modifier causes the copy, in some cases.
> Also, you'll get this performance hit if these are in any module/lib your using.
> There's a list of the offending libs on pg. 278, Mastering Reg Expressions.
> Of course some popular modules are on the list.
> > won't help.  Also, with the addition of \s* to my pattern (which I have
> I'm probably missing something, but why can't you just do 'length($1)',
> for $match_length?

The reason for this is that for this tag:

<!-- date -->

length($1) would give me 4 and length($&) would give me 13, which is
what I'm looking for.  I want to replace the entire tag, not just the

- Doug

Don't anthropomorphize computers. They hate that.

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