Hmmm, isdigit in C works on characters, not strings. Is that what you mean? In that case, you could do:

    $input =~ /^[[:digit:]]$/
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But if you want to know whether a string is "numeric", take a look at Regexp::Common, which has a bunch of regexes to determine whether a string contains a "number" - depending on what kind of number you are looking for (integer, signed integers, decimal numbers, floats, different bases, group separators, etc).

Abigail