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Testing if a variable is numeric

Posted by enquirer (enquirer), 8 August 2002
An email enquirer wrote:

How do I test if a variable is text or numeric?

If I want to do a printf and format for a specific width  I need to know if I should apply %s  , %f or  %d

Posted by admin (Graham Ellis), 8 August 2002
Perl variables are untyped - you don't declare them to hold any particular data type, and even future specifications of "int" and such like are going to be more designed as compiler hints.

I would tend to check a variable by writing
       if ($x =~ /^-?\d/) ....
to see if it contains a number, or perhaps
       if ($x =~ /^-?\d*\.) ...
to see if it contains a floating number.

There's further background on this in "Programming in Perl" by Larry Wall, Tom Christiansen and Jon Orwant, pages 58 and 59.

You might also like to look at the REF function whihc tells you if a scalar contains certain other types (e.g. object, reference).

This page is a thread posted to the opentalk forum at and archived here for reference. To jump to the archive index please follow this link.

Comment: "For a little more complete test for integers it may be a ..."
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Comment by dpminusa (published 2011-02-18)
For a little more complete test for integers it may be a best to use:

/^[+-]?\d+$/ otherwise values like 123abc test as numeric.

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