Extract leading numbers from a string in batch script

Question

I am new to batch scripting. although i have shell and python solutions for this problem but got stuck in batch script.

I have string like 123_happy,

Answer 1

I think this is the simplest way:

@echo off
setlocal

set "str=123_happy"
set /A num=str
echo Result = %num%

When set /A command get a value from a variable, it convert the number until the first non-digit character with no error.

To preserve left zeros:

set "str=0128_happy"
set "num=1%str%"
set /A num=num
set "num=%num:~1%"
echo Result = %num%