I think you shouldn't use the (?{...}) construct without a very good reason. To run some code on all matches of a regexp in a string, you can do this for example (untested):

while ($string =~ /(pattern)/g) {
    do_something_with($1);
}
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Or, if you want overlapping matches too, then

while ($string =~ /(?=(patter))/g) {
    do_something_with($1);
}
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