Re: How to test whether a string is a valid number?

[Andrew J. Schorr]

On Mon, Sep 07, 2020 at 10:38:16PM -0400, Andrew J. Schorr wrote:
> On Mon, Sep 07, 2020 at 07:00:42PM -0500, Peng Yu wrote:
> > I want to know whether a string is a valid number. But it seems typeof
> > is not appropriate for it? Is there something available in awk that
> > can tell whether a string is a valid number? Thanks.
> > 
> > $ awk -v x=5 -e  'BEGIN { print typeof(3.5),typeof(x) }'
> > number strnum
> 
> Typically, one tests the expression (x+0 == x),
> but that works only for user input. To be safe:
> 
> function isnumeric(x,   f) {
>    return (split(x, f, " ") == 1) && (f[1]+0 == f[1])
> }
> 
> Or if you feel that white-space padding renders it
> non-numeric, you could say:
> 
> function isnumeric(x,   f) {
>    return (split(x, f, " ") == 1) && (length(f[1]) == length(x)) && (f[1]+0 
> == f[1])
> }

Or maybe this might be more efficient:

function isnumeric(x,   f) {
   switch (typeof(x)) {
   case "number":
   case "strnum":
      return 1
   case "string":
      return (split(x, f, " ") == 1) && (length(f[1]) == length(x)) && (f[1]+0 
== f[1])
   default:
      return 0
   }
}

But the strnum type ignores leading & trailing whitespace, so you may want
to use the string test for that case also.

Regards,
Andy