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

User · Answer

A slightly more robust regex can be found in Regexp::Common.

It sounds like you want to know if Perl thinks a variable is numeric. Here's a function that traps that warning:

sub is_number{
  my $n = shift;
  my $ret = 1;
  $SIG{"__WARN__"} = sub {$ret = 0};
  eval { my $x = $n + 1 };
  return $ret
}

Another option is to turn off the warning locally:

{
  no warnings "numeric"; # Ignore "isn't numeric" warning
  ...                    # Use a variable that might not be numeric
}

Note that non-numeric variables will be silently converted to 0, which is probably what you wanted anyway.

User · Answer

Personally I think that the way to go is to rely on Perl s internal context to make the solution bullet-proof  A good regexp could match all the valid numeric values and none of the non-numeric ones  or vice versa   but as there is a way of employing the same logic the interpreter is using it should be safer to rely on that directly   As I tend to run my scripts with -w  I had to combine the idea of comparing the result of  value plus zero  to the original value with the no warnings based approach of  ysth   do        no warnings  numeric       if   x   0 ne  x    return  not numeric     else   return  numeric

User · Answer

The original question was how to tell if a variable was numeric  not if it  has a numeric value    There are a few operators that have separate modes of operation for numeric and string operands  where  numeric  means anything that was originally a number or was ever used in a numeric context  e g  in  x    123   0  x  before the addition   x is a string  afterwards it is considered numeric    One way to tell is this   if   length  do   no warnings  numeric    x  amp                 print   x is numeric n       If the bitwise feature is enabled  that makes  amp  only a numeric operator and adds a separate string  amp   operator  you must disable it   if   length  do   no if     gt   5 022   feature    bitwise   no warnings  numeric    x  amp                 print   x is numeric n        bitwise is available in perl 5 022 and above  and enabled by default if you use 5 028  or above

User · Answer

I don t believe there is anything builtin to do it   For more than you ever wanted to see on the subject  see Perlmonks on Detecting Numeric

User · Answer

rexep not perfect    this is   use Try  Tiny   sub is numeric     my   x          my  numeric   1    try       use warnings FATAL   gt  qw numeric       0    x        catch        numeric   0         return  numeric

User · Answer

You can use Regular Expressions to determine if  foo is a number  or not    Take a look here  How do I determine whether a scalar is a number

User · Answer

Check out the CPAN module Regexp  Common  I think it does exactly what you need and handles all the edge cases  e g  real numbers  scientific notation  etc   e g   use Regexp  Common  if   var      RE num  real      print q a number

User · Answer

Usually number validation is done with regular expressions  This code will determine if something is numeric as well as check for undefined variables as to not throw warnings   sub is integer      defined    0   amp  amp     0         -   d        sub is float      defined    0   amp  amp     0         -   d     d           Here s some reading material you should look at

User · Answer

Try this   If    x      D    amp  amp    x ne

User · Answer

A simple  and maybe simplistic  answer to the question is the content of  x numeric is the following   if   x  eq   x 0             It does a textual comparison of the original  x with the  x converted to a numeric value

User · Answer

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

User · Answer

if   defined  x  amp  amp   x    m  D       or  x   0 if    x  if    x    m  D       This is a slight variation on Veekay s answer but let me explain my reasoning for the change   Performing a regex on an undefined value will cause error spew and will cause the code to exit in many if not most environments  Testing if the value is defined or setting a default case like i did in the alternative example before running the expression will  at a minimum  save your error log

User · Answer

I found this interesting though  if    value   0 eq  value          A number     push  args   value    else         A string     push  args     value

User · Answer

Not perfect  but you can use a regex   sub isnumber        shift      -  d     d

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

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