$value = undef;
$value = (0 + "$1$3")
    if $thing =~ m/ ^
                  (\-|\+)?     # optional sign: $1
                  (\$)?        # optional dollar sign: $2
                  (
                    \d+        # at least one digit
                    (,\d\d\d)* # zero or more comma groups
                    (\.\d*)?   # optional fractional part
                  |
                    (\.\d+)    # only a fractional part
                  )            # the whole mantissa: $3
                  $ /x;
print "numeric! value = $value\n" if defined $value;