[FWP] Substitution

["Juanma Barranquero" <barranquero@laley-actualidad.es>]

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In a script a coworker of mine is writing, it is necessary to do the
following:

Substituting a substring ($pat) inside of a big (>500K) string
($text), but the first time it is changed to one thing ($s1) and
afterwards it is changed to another thing ($s2). Also, $s1 contains
the original $pat (in fact, it is $pat . $s2). So far, the best we've
been able to come with is:

$text =3D~ s/$pat/$s1/;
1 while ($text =3D~ s/$pat(.*?)$pat/$pat$1$s2/);

but obviously it is horribly inefficient.

Does someone know of a better/faster way? Is there any one-liner for
that?

                                                       /L/e/k/t/u


P.S.: I hope this is not against the spirit of Fun With Perl. I know
how implement it with index, etc., but it is very puzzling not being
able to find a regexp way to do that...

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