How to check if a parameter (or variable) is a number in a Batch script

Question

I need to check if a parameter that is passed to a Windows Batch file is a numeric value or not. It would be good for the check to also works for variables.

I found a

Answer 1

if errorlevel accepts only numeric values which can be used for a checks:

set test_var=001
( 
  (if errorlevel %test_var% break ) 2>nul
)&&(
  echo %test_var% is numeric
)||(
  echo %test_var% is NOT numeric
)

set test_var=001X
( 
  (if errorlevel %test_var% break ) 2>nul
)&&(
  echo %test_var% is numeric
)||(
  echo %test_var% is NOT numeric
)

the first check will pass, the second not. Though the script above would not handle unary + - if you want to handle this case too check - isInteger.bat