Question

To test whether a variable is e.g. a number greater than 0, you would write:

((i > 0))

But how would I test if the variable is not a number greater than 0?

EDIT

Sorry for the typo, meant not a number greater than 0.

EDIT 2

Sry for the poor question. The value of the variable is passed as a commandline argument, so it may be a number or not. This also needs to be checked.

Answer 1

For checking on not being number, you have to test with regex. I have used -5 instead 0 just to demonstrate more general case (My assumption is that you use integers):

#!/bin/bash

A=$1

if [[ $A =~ ^[\-0-9]+$ ]] && (( A > -5)); then
  echo "A is number and is greater then -5"
else
  echo "A is not a number or is <= -5"
fi

If you want to test for non-integers, you have to clarify in your question what is considered number.