Make an environment variable survive ENDLOCAL

environment-variables batch-file

Solution 1:

The ENDLOCAL & SET VAR=%TEMPVAR% pattern is classic. But there are situations where it is not ideal.

If you do not know the contents of TEMPVAR, then you might run into problems if the value contains special characters like < > & or|. You can generally protect against that by using quotes like SET "VAR=%TEMPVAR%", but that can cause problems if there are special characters and the value is already quoted.

A FOR expression is an excellent choice to transport a value across the ENDLOCAL barrier if you are concerned about special characters. Delayed expansion should be enabled before the ENDLOCAL, and disabled after the ENDLOCAL.

setlocal enableDelayedExpansion
set "TEMPVAR=This & "that ^& the other thing"
for /f "delims=" %%A in (""!TEMPVAR!"") do endlocal & set "VAR=%%~A"

Limitations:

  • If delayed expansion is enabled after the ENDLOCAL, then the final value will be corrupted if the TEMPVAR contained !.

  • values containing a lineFeed character cannot be transported

If you must return multiple values, and you know of a character that cannot appear in either value, then simply use the appropriate FOR /F options. For example, if I know that the values cannot contain |:

setlocal enableDelayedExpansion
set "temp1=val1"
set "temp2=val2"
for /f "tokens=1,2 delims=|" %%A in (""!temp1!"|"!temp2!"") do (
   endLocal
   set "var1=%%~A"
   set "var2=%%~B"
)

If you must return multiple values, and the character set is unrestricted, then use nested FOR /F loops:

setlocal enableDelayedExpansion
set "temp1=val1"
set "temp2=val2"
for /f "delims=" %%A in (""!temp1!"") do (
  for /f "delims=" %%B in (""!temp2!"") do (
    endlocal
    set "var1=%%~A"
    set "var2=%%~B"
  )
)

Definitely check out jeb's answer for a safe, bullet proof technique that works for all possible values in all situations.

2017-08-21 - New function RETURN.BAT
I've worked with DosTips user jeb to develop a batch utility called RETURN.BAT that can be used to exit from a script or called routine and return one or more variables across the ENDLOCAL barrier. Very cool :-)

Below is version 3.0 of the code. I most likely will not keep this code up-to-date. Best to follow the link to make sure you get the latest version, and to see some example usage.

RETURN.BAT

::RETURN.BAT Version 3.0
@if "%~2" equ "" (goto :return.special) else goto :return
:::
:::call RETURN  ValueVar  ReturnVar  [ErrorCode]
:::  Used by batch functions to EXIT /B and safely return any value across the
:::  ENDLOCAL barrier.
:::    ValueVar  = The name of the local variable containing the return value.
:::    ReturnVar = The name of the variable to receive the return value.
:::    ErrorCode = The returned ERRORLEVEL, defaults to 0 if not specified.
:::
:::call RETURN "ValueVar1 ValueVar2 ..." "ReturnVar1 ReturnVar2 ..." [ErrorCode]
:::  Same as before, except the first and second arugments are quoted and space
:::  delimited lists of variable names.
:::
:::  Note that the total length of all assignments (variable names and values)
:::  must be less then 3.8k bytes. No checks are performed to verify that all
:::  assignments fit within the limit. Variable names must not contain space,
:::  tab, comma, semicolon, caret, asterisk, question mark, or exclamation point.
:::
:::call RETURN  init
:::  Defines return.LF and return.CR variables. Not required, but should be
:::  called once at the top of your script to improve performance of RETURN.
:::
:::return /?
:::  Displays this help
:::
:::return /V
:::  Displays the version of RETURN.BAT
:::
:::
:::RETURN.BAT was written by Dave Benham and DosTips user jeb, and was originally
:::posted within the folloing DosTips thread:
:::  http://www.dostips.com/forum/viewtopic.php?f=3&t=6496
:::
::==============================================================================
::  If the code below is copied within a script, then the :return.special code
::  can be removed, and your script can use the following calls:
::
::    call :return   ValueVar  ReturnVar  [ErrorCode]
::
::    call :return.init
::

:return  ValueVar  ReturnVar  [ErrorCode]
:: Safely returns any value(s) across the ENDLOCAL barrier. Default ErrorCode is 0
setlocal enableDelayedExpansion
if not defined return.LF call :return.init
if not defined return.CR call :return.init
set "return.normalCmd="
set "return.delayedCmd="
set "return.vars=%~2"
for %%a in (%~1) do for /f "tokens=1*" %%b in ("!return.vars!") do (
  set "return.normal=!%%a!"
  if defined return.normal (
    set "return.normal=!return.normal:%%=%%3!"
    set "return.normal=!return.normal:"=%%4!"
    for %%C in ("!return.LF!") do set "return.normal=!return.normal:%%~C=%%~1!"
    for %%C in ("!return.CR!") do set "return.normal=!return.normal:%%~C=%%2!"
    set "return.delayed=!return.normal:^=^^^^!"
  ) else set "return.delayed="
  if defined return.delayed call :return.setDelayed
  set "return.normalCmd=!return.normalCmd!&set "%%b=!return.normal!"^!"
  set "return.delayedCmd=!return.delayedCmd!&set "%%b=!return.delayed!"^!"
  set "return.vars=%%c"
)
set "err=%~3"
if not defined err set "err=0"
for %%1 in ("!return.LF!") do for /f "tokens=1-3" %%2 in (^"!return.CR! %% "") do (
  (goto) 2>nul
  (goto) 2>nul
  if "^!^" equ "^!" (%return.delayedCmd:~1%) else %return.normalCmd:~1%
  if %err% equ 0 (call ) else if %err% equ 1 (call) else cmd /c exit %err%
)

:return.setDelayed
set "return.delayed=%return.delayed:!=^^^!%" !
exit /b

:return.special
@if /i "%~1" equ "init" goto return.init
@if "%~1" equ "/?" (
  for /f "tokens=* delims=:" %%A in ('findstr "^:::" "%~f0"') do @echo(%%A
  exit /b 0
)
@if /i "%~1" equ "/V" (
  for /f "tokens=* delims=:" %%A in ('findstr /rc:"^::RETURN.BAT Version" "%~f0"') do @echo %%A
  exit /b 0
)
@>&2 echo ERROR: Invalid call to RETURN.BAT
@exit /b 1


:return.init  -  Initializes the return.LF and return.CR variables
set ^"return.LF=^

^" The empty line above is critical - DO NOT REMOVE
for /f %%C in ('copy /z "%~f0" nul') do set "return.CR=%%C"
exit /b 0

Solution 2:

@ECHO OFF  
SETLOCAL  

REM Keep in mind that BAR in the next statement could be anything, including %1, etc.  
SET FOO=BAR  

ENDLOCAL && SET FOO=%FOO%

Solution 3:

The answer of dbenham is a good solution for "normal" strings, but it fails with exclamation marks ! if delayed expansion is enabled after ENDLOCAL (dbenham said this too).

But it will always fail with some tricky contents like embedded linefeeds,
as the FOR/F will split the content into multiple lines.
This will result into strange behaviour, the endlocal will executed multiple times (for each line feed), so the code isn't bullet proof.

There exists bullet proof solutions, but they are a bit messy :-)
A macro version exists SO:Preserving exclamation ..., to use it is easy, but to read it is ...

Or you could use a code block, you can paste it into your functions.
Dbenham and I developed this technic in the thread Re: new functions: :chr, :asc, :asciiMap,
there are also the explanations for this technic

@echo off
setlocal EnableDelayedExpansion
cls
for /f %%a in ('copy /Z "%~dpf0" nul') do set "CR=%%a"
set LF=^


rem TWO Empty lines are neccessary
set "original=zero*? %%~A%%~B%%~C%%~L!LF!one&line!LF!two with exclam^! !LF!three with "quotes^&"&"!LF!four with ^^^^ ^| ^< ^> ( ) ^& ^^^! ^"!LF!xxxxxwith CR!CR!five !LF!six with ^"^"Q ^"^"L still six "

setlocal DisableDelayedExpansion
call :lfTest result original

setlocal EnableDelayedExpansion
echo The result with disabled delayed expansion is:
if !original! == !result! (echo OK) ELSE echo !result!

call :lfTest result original
echo The result with enabled delayed expansion is:
if !original! == !result! (echo OK) ELSE echo !result!
echo ------------------
echo !original!

goto :eof

::::::::::::::::::::
:lfTest
setlocal
set "NotDelayedFlag=!"
echo(
if defined NotDelayedFlag (echo lfTest was called with Delayed Expansion DISABLED) else echo lfTest was called with Delayed Expansion ENABLED
setlocal EnableDelayedExpansion
set "var=!%~2!"

rem echo the input is:
rem echo !var!
echo(

rem ** Prepare for return
set "var=!var:%%=%%~1!"
set "var=!var:"=%%~2!"
for %%a in ("!LF!") do set "var=!var:%%~a=%%~L!"
for %%a in ("!CR!") do set "var=!var:%%~a=%%~3!"

rem ** It is neccessary to use two IF's else the %var% expansion doesn't work as expected
if not defined NotDelayedFlag set "var=!var:^=^^^^!"
if not defined NotDelayedFlag set "var=%var:!=^^^!%" !

set "replace=%% """ !CR!!CR!"
for %%L in ("!LF!") do (
   for /F "tokens=1,2,3" %%1 in ("!replace!") DO (
     ENDLOCAL
     ENDLOCAL
     set "%~1=%var%" !
     @echo off
      goto :eof
   )
)
exit /b

Solution 4:

I want to contribute to this too and tell you how you can pass over an array-like set of variables:

@echo off
rem clean up array in current environment:
set "ARRAY[0]=" & set "ARRAY[1]=" & set "ARRAY[2]=" & set "ARRAY[3]="
rem begin environment localisation block here:
setlocal EnableExtensions
rem define an array:
set "ARRAY[0]=1" & set "ARRAY[1]=2" & set "ARRAY[2]=4" & set "ARRAY[3]=8"
rem `set ARRAY` returns all variables starting with `ARRAY`:
for /F "tokens=1,* delims==" %%V in ('set ARRAY') do (
    if defined %%V (
        rem end environment localisation block once only:
        endlocal
    )
    rem re-assign the array, `for` variables transport it:
    set "%%V=%%W"
)
rem this is just for prove:
for /L %%I in (0,1,3) do (
    call echo %%ARRAY[%%I]%%
)
exit /B

The code works, because the very first array element is queried by if defined within the setlocal block where it is actually defined, so endlocal is executed once only. For all the successive loop iterations, the setlocal block is already ended and therefore if defined evaluates to FALSE.

This relies on the fact that at least one array element is assigned, or actually, that there is at least one variable defined whose name starts with ARRAY, within the setlocal/endlocal block. If none exist therein, endlocal is not going to be executed. Outside of the setlocal block, no such variable must be defined, because otherwise, if defined evaluates to TRUE more than once and therefore, endlocal is executed multiple times.

To overcome this restrictions, you can use a flag-like variable, according to this:

  • clear the flag variable, say ARR_FLAG, before the setlocal command: set "ARR_FLAG=";
  • define the flag variable inside of the setlocal/endlocal block, that is, assign a non-empty value to it (immediately before the for /F loop preferrably): set "ARR_FLAG=###";
  • change the if defined command line to: if defined ARR_FLAG (;
  • then you can also do optionally:
    • change the for /F option string to "delims=";
    • change the set command line in the for /F loop to: set "%%V";

Solution 5:

Something like the following (I haven't tested it):

@echo off 
setlocal 

set base=compute directory 
set pkg=compute sub-directory 
set scripts=%base%\%pkg%\Scripts 

pushd %scripts%

endlocal 

call .\activate.bat 
popd

Since the above doesn't work (see Marcelo's comment), I would probably do this as follows:

set uniquePrefix_base=compute directory 
set uniquePrefix_pkg=compute sub-directory 
set uniquePrefix_scripts=%uniquePrefix_base%\%uniquePrefix_pkg%\Scripts 
set uniquePrefix_base=
set uniquePrefix_pkg=

call %uniquePrefix_scripts%\activate.bat
set uniquePrefix_scripts=

where uniquePrefix_ is chosen to be "almost certainly" unique in your environment.

You could also test on entry to the bat file that the "uniquePrefix_..." environment variables are undefined on entry as expected - if not you can exit with an error.

I don't like copying the BAT to the TEMP directory as a general solution because of (a) the potential for a race condition with >1 caller, and (b) in the general case a BAT file might be accessing other files using a path relative to its location (e.g. %~dp0..\somedir\somefile.dat).

The following ugly solution will solve (b):

setlocal

set scripts=...whatever...
echo %scripts%>"%TEMP%\%~n0.dat"

endlocal

for /f "tokens=*" %%i in ('type "%TEMP%\%~n0.dat"') do call %%i\activate.bat
del "%TEMP%\%~n0.dat"

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