Batch File input validation - Make sure user entered an integer

Question

I\'m experimenting with a Windows batch file to perform a simple operation which requires the user to enter a non-negative integer. I\'m using simple batch-file techniques t

Answer 1

You're probably not doing this in a DOS batch file. Or at least, support for set /p is unheard of for me in DOS :-)

You could use substrings. In fact I have written a parser for a specific regular language that way once, but it's cumbersome. The easiest way would probably be to assign the contents of %userinput% to another variable, using set /a. If the result comes out as 0 you need to check whether the input itself was 0, otherwise you can conclude it was a non-number:

@echo off
setlocal enableextensions enabledelayedexpansion
set /p UserInput=Enter a number: 
set /a Test=UserInput
if !Test! EQU 0 (
  if !UserInput! EQU 0 (
    echo Number
  ) else (
    echo Not a number
  )
) else (
  echo Number
)

However, this works only for numbers in the range of Int32. If you just care for any number (possibly floating-point as well) then you need to resort to the loop-based approach of dissecting it.

NOTE: Updated to solve the space issues. However, there is still a problem lurking: Entering 123/5 yields "number", since set /a can evaluate this ...