You could also use a zero width lookahead. Just leave one character out of the zero width lookahead to increment pos().

use strict;
my $mystring = "AABAABAA";
my @array;
{} while $mystring =~ /A(?=ABAA)(?{push @array, pos($mystring)})/g;
print join(",", @array),"\n";

#or without any fancy "experimental" regex stuff

@array=();
while ($mystring =~ /A(?=ABAA)/g) {
    push @array, pos($mystring)
}
print join(",", @array),"\n";

__OUTPUTS__

1,4
1,4
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That is the 1 based position shown in the original post. If you want 0 based just use push @array, pos($mystring)-1