Change it to :

use Scalar::Util qw( looks_like_number );
if( ! looks_like_number( $VAR1 ) ) {
  do something...
}
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If your definition of a number needs to be more restrictive than looks_like_number, let us know what we can do to help you refine the test further.

Scalar::Util is a core module; it comes with Perl as part of the standard distribution.