How do I tell if a variable has a numeric value in Perl?

Question

Is there a simple way in Perl that will allow me to determine if a given variable is numeric? Something along the lines of:

if (is_number($x)) { ... } 

would be ideal. A technique that won't throw warnings when the -w switch is being used is certainly preferred.

Answer 1

Use Scalar::Util::looks_like_number() which uses the internal Perl C API's looks_like_number() function, which is probably the most efficient way to do this. Note that the strings "inf" and "infinity" are treated as numbers.

Example:

#!/usr/bin/perl  use warnings; use strict;  use Scalar::Util qw(looks_like_number);  my @exprs = qw(1 5.25 0.001 1.3e8 foo bar 1dd inf infinity);  foreach my $expr (@exprs) {     print "$expr is", looks_like_number($expr) ? '' : ' not', " a number\n"; } 

Gives this output:

1 is a number 5.25 is a number 0.001 is a number 1.3e8 is a number foo is not a number bar is not a number 1dd is not a number inf is a number infinity is a number 

See also:

• perldoc Scalar::Util
• perldoc perlapi for looks_like_number