Why are environment variables not updating within FOR loop?

Question

I have a batch file that is scanning a file URLs.txt and for each url run it and download the file. The issue I have is the environment variable within the FOR loop. I am using cat, sed and awk to get the last two parts of the the url so I can provide the filename. The issue is the environment variable is never updated after the first run. I can see that tmp2.txt just updated correctly for every url, but the batch file is not updating outfile and thus I keep overwriting the first file.

I tried to simplify the batch file for a test and any variable within a for loop never seems to update.

@echo off
setlocal enabledelayedexpansion

for /F "tokens=*" %%A in (URLs.txt) do (
    echo %%A > tmp.txt
    cat tmp.txt | sed "s/\(.*\)\//\1_/" | awk -F "/" "{print $NF}" > tmp2.txt
    set /p outfile=<tmp2.txt
    echo Varible A
    echo %%A
    echo.
    echo Varible outfile
    echo %outfile%
    call curl.exe -o %outfile% -u username:password --insecure %%A
    pause
)

Why is environment variable outfile not updated within FOR loop?

Ah, the classic "you're using delayed expansion, but you're not using delayed expansion." It happens more than you might think. — SomethingDark
– SomethingDark, Commented Oct 31, 2016 at 2:13

Magoo · Accepted Answer · 2016-10-31 01:22:37Z

echo !outfile!

Within a block statement (a parenthesised series of statements), the entire block is parsed and then executed. Any %var% within the block will be replaced by that variable's value at the time the block is parsed - before the block is executed - the same thing applies to a FOR ... DO (block).

Hence, IF (something) else (somethingelse) will be executed using the values of %variables% at the time the IF is encountered.

Two common ways to overcome this are 1) to use setlocal enabledelayedexpansion and use !var! in place of %var% to access the changed value of var or 2) to call a subroutine to perform further processing using the changed values.

Note therefore the use of CALL ECHO %%var%% which displays the changed value of var. CALL ECHO %%errorlevel%% displays, but sadly then RESETS errorlevel.

In your case, since outfile is assigned the value %%A, you can replace %outfile% with %%A - and it would be an idea to "quote the string" anyway since "quoting a string" makes it a single token rather than a series - just in case your filenames contain separators like Space

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