Enable and Disable Delayed Expansion, what does it do?

Question

I\'ve seen SETLOCAL ENABLEDELAYEDEXPANSION & SETLOCAL DISABLEDELAYEDEXPANSION in many batch files but what do the commands actually do?

Answer 1

Copied from How do you use SETLOCAL in a batch file? (as dbenham indicated in his first comment).

Suppose this code:

If "%getOption%" equ  "yes" (
   set /P option=Enter option: 
   echo Option read: %option%
)

Previous code will NOT work becase %option% value is replaced just one time when the IF command is parsed (before it is executed). You need to "delay" variable value expansion until SET /P command had modified variable value:

setlocal EnableDelayedExpansion
If "%getOption%" equ  "yes" (
   set /P option=Enter option: 
   echo Option read: !option!
)

Check this:

set var=Before
set var=After & echo Normal: %var%  Delayed: !var!

The output is: Normal: Before Delayed: After