Batch - Recurse directories from a variable and expand results in another variable - batch-file

Question

I'm creating a simple production environment for work and in doing so need to set specific environment variables for specific projects in batch file.
Here's what i want to achieve:
1) Define a single environment variable which would define a list of directories
2) Recurse down each directory and add all leaf folders to a final environment variable.
[EDIT] After looking back at what i originally posted i was able to remove some redundancy. But the "The input line is too long." error occurs when %LINE% gets too long. Using the short path expansion does help but it can still error out. I'll look at how to break the echo to a temp file next as suggested.
Here's what i currently have:
#echo off
set RECURSE_THESE_DIRS=C:\Users\eric\Autodesk
set TMP_FILE=%CD%TMP_FILE.%RANDOM%.txt
setLocal EnableDelayedExpansion
for %%i in (%RECURSE_THESE_DIRS%) do (
if exist %%~si\NUL (
for /f "tokens=*" %%G in ('dir /b /s /a:d %%i') do set LIST=!LIST!;%%G
)
)
set LIST=%LIST:~1%
rem !!! AT THE ECHO LINE BELOW IF %LIST% IS TOO LONG, THIS SCRIPT FAILS
rem !!! WITH The input line is too long. ERROR :(
echo %LIST%>%TMP_FILE%
endlocal
for /F "delims=" %%G in (%TMP_FILE%) do set FINAL_VAR=%%G
del /F %TMP_FILE%
So by setting RECURSE_THESE_DIRS to directories i wish to parse, i end up with a %FINAL_VAR% which i can use to specify paths for proprietary software i use. Or i could use this script to append to %PATH%, etc...
This works for me but i would love suggestions to improve/streamline my script?

Answer 1

The root of your problem is that batch is limited to fit the variable name, contents and = into 8192 bytes, hence your directory-list simply isn't going to fit into one variable.
Personally, I'd just spit out a dir/s/b/a-d list to a tempfile and process that file with a for/f "delims=" - after all, you'd be likely to need to process your ;-separated envvar similarly in whatever process you are proposing to execute.
For instance, here's a test producing the same error - not using filenames at all
#ECHO OFF
SETLOCAL
SET "var=hello!1234"
SET var=%var%%var%%var%%var%%var%
SET var=%var%%var%%var%%var%%var%%var%%var%%var%
SET var=%var%%var%%var%%var%%var%
SET var=%var%%var%%var%%var%
SET count=8000
:loop
SET /a count +=1
ECHO %count%
SET var=%var%x
ECHO %var%
GOTO loop
GOTO :EOF
This should fail where count=8184.

Answer 2

Suggestions:
Use for /d /r to handle the recursion
Maybe i'm wrong, but in your script, you traverse the directory hierarchy, adding each directory to temp file which is then readed to concatenate its lines into a variable which is then writed to temp file, to be read again in another variable. If concatenation of directories fit into a variable, why not concatenate them without any temporary file?
If concatenation is in the limit of line length, as suggested by npocmaka, and if soported by end application, user short paths. Also, instead of adding the new values in the same instruction (not line) that contains the for loop, use a call to a subrutine with the new value passed to it, and then append the value. It's slower, but command lines executed will be shorter.