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tells us: Test if the content of an SV looks like a number (or is a number)."Inf" and "Infinity" are treated as numbers (so will not issue a non-numeric warning), even if your atof() doesn't grok them. The description in Scalar:: Util is fine, looks_like_number tells you if your input is something that Perl would treat as a number, which is not necessarily the best answer for this question.

Plus, Scalar:: Util can handle "0 but true" which is a valid Perl number -- something your regular expression might not handle.

Constructing a single regular expression to validate a number is really difficult. Perlfaq4 contains a section "How do I determine whether a scalar is a number/whole/integer/float?

But a single malicious user or prankster might enter a string into the age field, and an incomplete e-mail address into the address field.

If you don't have a data validation routine guarding the entrance to your database, this incorrect data might get saved and cause you all manner of heartache later (can't you just see My SQL spitting out "illegal data type" errors? Input validation is a necessary safeguard to the integrity of your application database.

The code from that documentation shows the following tests: So if you were using those tests (excluding the first one) you would have to verify that one or more of the tests passes. Another method, since you don't want to use the module Scalar:: Util, you can learn from the code IN Scalar:: Util.

The looks_like_number() function is set up like this: Yes, it appears that Scalar-List-Utils-1.23 had a pure Perl version, whereas Scalar-List-Utils-1.23_03 does not.If you use Perl, this task is made simpler by the CGI:: Validate module, which provides a bunch of built-in methods to verify the data entered by the user.If you've used Getopt:: Long before, you know it can be used to read and validate command-line arguments to a Perl script.One thing that the post implies but doesn't make explicit is that "number" really means "non-negative integer". It's part of the STANDARD Perl library and thus is almost always available for programming use.Many cases, including scientific notation, are hardly simple. My variant, considering scientific notation, too: /^[ -]? As I tend to run my scripts with if ( defined $x && $x ! Performing a regex on an undefined value will cause error spew and will cause the code to exit in many if not most environments.

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