FAQ 4.73 How do I determine whether a scalar is a number/whole/integer/float?


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4.73: 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:

use 5.010;

given( $number ) {
when( /\D/ )
{ say "\thas nondigits"; continue }
when( /^\d+\z/ )
{ say "\tis a whole number"; continue }
when( /^-?\d+\z/ )
{ say "\tis an integer"; continue }
when( /^[+-]?\d+\z/ )
{ say "\tis a +/- integer"; continue }
when( /^-?(?:\d+\.?|\.\d)\d*\z/ )
{ say "\tis a real number"; continue }
when( /^[+-]?(?=\.?\d)\d*\.?\d*(?:e[+-]?\d+)?\z/i)
{ say "\tis a C float" }

There are also some commonly used modules for the task. Scalar::Util
(distributed with 5.8) provides access to perl's internal function
"looks_like_number" for determining whether a variable looks like a
number. Data::Types exports functions that validate data types using
both the above and other regular expressions. Thirdly, there is
"Regexp::Common" which has regular expressions to match various types of
numbers. Those three modules are available from the CPAN.

If you're on a POSIX system, Perl supports the "POSIX::strtod" function.
Its semantics are somewhat cumbersome, so here's a "getnum" wrapper
function for more convenient access. This function takes a string and
returns the number it found, or "undef" for input that isn't a C float.
The "is_numeric" function is a front end to "getnum" if you just want to
say, "Is this a float?"

sub getnum {
use POSIX qw(strtod);
my $str = shift;
$str =~ s/^\s+//;
$str =~ s/\s+$//;
$! = 0;
my($num, $unparsed) = strtod($str);
if (($str eq '') || ($unparsed != 0) || $!) {
return undef;
else {
return $num;

sub is_numeric { defined getnum($_[0]) }

Or you could check out the String::Scanf module on the CPAN instead. The
"POSIX" module (part of the standard Perl distribution) provides the
"strtod" and "strtol" for converting strings to double and longs,


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