How do i replace a character with another character in batch?

Question

I need to replace all I's in a variable %ps% with 1's and send the output to another variable %ps2%

Answer 1

as single replacements, just a simple:

set "ps2=%ps:I=1%"

for multiple replacements either specify new lines for each or you could run a for loop, but you'll need to define the search replace items regardless:

@echo off
setlocal enabledelayedexpansion
set "ps=Iab"
set "search_rep="I=1","a=2","b=4""
if not defined ps2 set "ps2=%ps%"
for %%i in (%search_rep%) do set "ps2=!ps2:%%~i!"
echo %ps2%

Take note of the use of delayedepansion in the above example.