Question

I need to detect whether a value input by a user contains a positive, non-zero number. The input field represents a product quantity, and must be greater than zero, and contain no alpha or non-numeric characters. IOW, the input must contains only these characters: 0123456789 But of course, zero by itself is not acceptable. Here’s how I am using the code:

  if( $fields{'quantity'} =~ [this is where I am unsure]  )
  {
    $errors .= "Please enter a whole number for the quantity.";
  }

Thanks.

Answer 1

Remember that strings like 1E4 are also numeric, so not every number has to contain [0-9] only.

The looks_like_number function provided by Scalar::Util is the Right Way to check if a variable is numeric.

use Scalar::Util 'looks_like_number';

if ( not looks_like_number( $fields{quantity} ) or $fields{quantity} <= 0 ) {

    warn "Please enter a whole number for the quantity";
}

The same thing more succinctly:

warn "Please enter a whole number for the quantity"
  unless looks_like_number( $fields{quantity} )
         && $fields{quantity} > 0;

Be warned that strings like Nan, Inf and Infinity are also deemed numeric, so you may want to consider weeding those out as well:

warn "Please enter a whole number for the quantity"
  unless looks_like_number( $fields{quantity} )
         && $fields{quantity} !~ /Inf|NaN/i
         && $fields{quantity} > 0;