This does work as advertised but probably different than you thought. You should have used warnings ;-), your regex is equivalent to $data =~ s/aa//g; and that is not what you had in mind, is it? A small typo is the cause, you print a but I think wanted to print 'a', the letter 'a' and not nothing to the filehandle a.

The important point is, pos() does not work with the substitution operator, only with m//g. See pos.

So I guess we have to make do with the  1 while s/// solution.

-- Hofmator