Might want to trim leading 0s off the argument, being careful not to trim a simple 0 to the empty string. And Perl will do the "right thing" with a leading +

  DB<175> $av0="+10"

  DB<176> say sprintf("%u", $av0)
10
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I don't want to anticipate all the stuff Perl might do to an argument on the way to treating it as a number. I think Math::BigInt may be the (conceptually) simplest thing.