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

Just another option

@echo off
    setlocal enableextensions disabledelayedexpansion

    call :extractLeadingNumbers 123_happy leadingNumbers
    echo %leadingNumbers%

    call :extractLeadingNumbers 234.healthy leadingNumbers
    echo %leadingNumbers%

    call :extractLeadingNumbers "3456wealthy" leadingNumbers
    echo %leadingNumbers%

    goto :eof


rem This extracts the first numerical serie in the input string    
:extractLeadingNumbers inputString returnVar
    setlocal enableextensions disabledelayedexpansion
    rem Retrieve the string from arguments
    set "string=%~1"

    rem Use numbers as delimiters (so they are removed) to retrieve the rest of the string
    for /f "tokens=1-2 delims=0123456789 " %%a in ("%string:^"=%") do set "delimiters=%%a%%b"

    rem Use the retrieved characters as delimiters to retrieve the first numerical serie
    for /f "delims=%delimiters% " %%a in ("%string:^"=%") do set "numbers=%%a"

    rem Return the found data to caller and leave
    endlocal & set "%~2=%numbers%"
    goto :eof