Question

I have a hard time understanding the following batch script:

@echo off
echo b>b.txt
for /f %%A in ('echo b.txt b.txt') do (
    echo %%A
    if not exist %%A (
        echo does not exist.
    ) else (
        echo %%A exist.
    )
)

In the beginning, I make sure that a file “b.txt” exists, and then I would expect the loop to output twice the name of this file, and that it exists. However, the actual output that I get is:

b.txt
does not exists

Can someone explain this behavior?

Answer 1

Just as suggestion you may try to assign file name to variable just to make sure you reference exactly same thing in both statements, like this:

set file=b.txt
echo b>%file%
for /f %%A in ('echo %file% ^& echo %file%') do (
    echo [%%A]
    if  not exist %%A (
        echo [%%A] does not exist.
    ) else (
        echo [%%A] exist.
    )
)

I also removed echo off so you would see expansion output, and put brackets around %%A to see it’s boundary

Edit: some addtional troubleshooting:
I would probably start building the script up from command line, changing only only one thing at a time and see where it breaks.

if b.txt exist echo Exists

If it works then

for /f %A in ('echo whatever') if b.txt exist echo Exists

and so on, up to

for /f %A in ('echo b.txt ^&echo b.txt') do (if exist %A (echo %A exists) else (echo not exists))

You could also use different for variant (although I cannot see how it could make a difference):

for %A in (b.txt b.txt) do (if exist %A (echo %A Exists) else (echo not exists))