Here's a somewhat hacky solution, but it seems to work: 
use strict;
use warnings;
use 5.010;

my $string = 'foobar';

while ($string =~ s/\G.*?\K[aeiou]/\U$&/si) {
    say $&;
} continue {
    pos($string) = $+[-1];
}
say $string;

[download]

The trick is to manually set pos, and then use \G in the regex to anchor to that position. But since you want to match anything after that (and not just exactly at the current position), you need a .*? (and the /s modifier if newlines are in the string).

Now it matches too much text, but the \K assertion cuts off the start of the match, making $& what it should be.

\K requires perl 5.10.0, but since that's the third-oldest major perl 5 release, that shouldn't be a problem. It's not 1995 after all :-)

Insert generic warning about the runtime overhead of $& here, and how it's better to extract it with substr, @+ and @-.

Perl 6 - second systems done right

In reply to Re: Loop through global substitution by moritz
in thread Loop through global substitution by alafarm

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.