There is a very good chapter "NUMBERS" in the Perl Cookbook by Tom Christiansen & Nathan Torkington. This book is a very good starting point for Perl newbies if they are are no programming beginners.

Here are some precooked solutions (the cookbook's equivalent of just-a
+dd-water meals) for most common cases.

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