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How do I determine whether a scalar is a number/whole/integer/float?

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How do I determine whether a scalar is a number/whole/integer/float?

Assuming that you don't care about IEEE notations like ``NaN'' or ``Infinity'', you probably just want to use a regular expression.

   warn "has nondigits"        if     /\D/;
   warn "not a whole number"   unless /^\d+$/;
   warn "not an integer"       unless /^-?\d+$/;  # reject +3
   warn "not an integer"       unless /^[+-]?\d+$/;
   warn "not a decimal number" unless /^-?\d+\.?\d*$/;  # rejects .2
   warn "not a decimal number" unless /^-?(?:\d+(?:\.\d*)?|\.\d+)$/;
   warn "not a C float"
       unless /^([+-]?)(?=\d|\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?$/;

Or you could check out http://www.perl.com/CPAN/modules/by-module/String/String-Scanf-1.1.tar.gz instead. The POSIX module (part of the standard Perl distribution) provides the strtol and strtod for converting strings to double and longs, respectively.

Source: Perl FAQ: Data Manipulation
Copyright: Copyright (c) 1997 Tom Christiansen and Nathan Torkington.

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