Batch : Why does for loop return empty when it is placed in if else clause?

Question

I have this code in my .bat file:

@echo off
setlocal enableextensions disabledelayedexpansion

//Run sqlcmd command to backup file

//error handler for sqlcmd
if %ERRORLEVEL% == 0(
    FOR /F "delims=|" %%I IN ('DIR /s "D:\Temp\*.bak" /b /O:D') DO set latestFile=%%I
    echo %latestFile%
) else (
    echo Error occured.
)

Problem

The result that I always got from echo %latestFile% is always ECHO is off meaning, the %%I is empty. However, when I move the for loop to outside of the if-else clause and used goto to execute the for loop, this problem does not occur.

You're explicitly turning off delayed expansion, and then running a command that needs delayed expansion. Enable it and then use echo !latestFile! See blogs.msdn.microsoft.com/oldnewthing/20060823-00/?p=29993 — Ryan Bemrose
– Ryan Bemrose, Commented Feb 28, 2017 at 3:42

Ryan Bemrose · Accepted Answer · 2017-02-28 04:04:30Z

By default, the CMD parser reads and parses an entire statement block inside parentheses before executing it. This means all variable expansion in the entire block happens before any commands are run. Here is a deeper explanation why this works this way.

To get around this, CMD supports Delayed Expansion, which allows variables to be re-parsed before each line in a statement block. The syntax for this is !variable!.

First, you need to enable delayed expansion, by changing your setlocal line from disabledelayedexpansion to enabledelayedexpansion. Second, you need to change your echo line to use ! instead of %

REM @echo off
setlocal enableextensions enabledelayedexpansion

//Run sqlcmd command to backup file

//error handler for sqlcmd
if %ERRORLEVEL% == 0(
    FOR /F "delims=|" %%I IN ('DIR /s "D:\Temp\*.bak" /b /O:D') DO set latestFile=%%I
    echo !latestFile!
) else (
    echo Error occured.
)

Finally, note that @echo off suppresses debugging information, and you should always remove or comment that line while debugging. It often makes the difference between having to guess which line failed and knowing.

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