Concatenating files in a Batch script

Question

I have a batch script that would concatenate the content of files that were listed in an index file. It used to work until there were spaces in the paths. I have edited it a bit, but it is something like this:

SET INPUT="C:\Has Spaces In Path\indexfile.txt"
SET ROOT="C:\Has Spaces In Path\inputdirectory\"
SET OUTPUT="C:\Has Spaces In Path\outputdirectory\mergedfile.txt"

FOR /F %%A IN (%INPUT%) DO TYPE "%ROOT%%%A" >> "%OUTPUT%"

The problem I have is that %INPUT% now appears to get tokenised in the for loop and if I put quotes around it (i.e. "%INPUT%") it does not work either. Is there any way I can get this loop to iterate over each line in the file specified by INPUT and concatenate the contents to the OUTPUT file?

Thanks.

Edit: Based on the answer, this did what I wanted:

FOR /F %%A IN ('type "%INPUT%"') DO TYPE "%ROOT%%%A" >> "%MERGED%"

Answer 1

FOR /F %%A IN ('type %INPUT%') DO echo %%A

' in the brackets will cause to execute the statement and uses the output like a file source

Answer 2

FOR /F "usebackq" %%A IN ("%INPUT%") DO TYPE "%ROOT%%%A" >> "%OUTPUT%"

or, better yet:

(FOR /F "usebackq" %%A IN ("%INPUT%") DO TYPE "%ROOT%%%A") > "%OUTPUT%"

For further details, see: FOR /?