A limited method, but one that could be built on is to use +0. Using an eval like the example below will return 0 if fed a string containing no numeric characters or the number 0 so, something like this could be a start:

  foreach my $var ('0', '-112.04', 'qwerty') {
        $var2 = eval '$var+0';

        if($var eq '0' or $var2) {
                print "Is an number\n";
        } else {
                print "May not be an number\n";
        }
}
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$japh->{'Caillte'} = $me;