How to set PATH environment variable in batch file only once on Windows? -

i have batch file sets user path , run part of visual studio ide build step.

@echo off @echo %path% set comspec = "%vcinstalldir%\vcvarsall.bat" amd64 setx path "..\..\lib\libsndfile;..\..\lib\simulink"  @echo %path% 

when build project, close vs, , reopen it, , rebuild, see appended path part of path variable. however, see in windows setting of environment variable path variable created under user environment variables as

..\..\lib\libsndfile;..\..\lib\simulink 

question 1:

why path appear appended path part of system environment variable?

on executing echo %path% through visual studio console (when run project second times) prints system variable path , new path created appended it.

question 2:

i want modify batch file sets once path environment variable in user settings during first run of visual studio build. if user variable path exists on subsequent runs, should not execute set command again avoid appending new path again , again in system variable.

any ideas how achieve this?

edit: after testing, appears original answer isn't entirely applicable op's questions. answer op more directly:

1. %path% combines values in hklm\system\currentcontrolset\control\session manager\environment\path hkcu\environment\path. when setx "dir;dir", you're setting hkey_current_user path value. machine-wide hkey_local_machine path value remains untouched. that's why see values appended, rather replacements. you'd have use setx /m replace hklm path value. but please don't unless want create severe problems operating system installation.

2. if want test whether directory exists in %path%, cd or pushd both directory want check , each directory within %path% unify each, making sure relative paths, environment variables, etc. flattened. set "var=%cd%" each. if /i "!dir1!"=="!dir2!" directory exists somewhere in %path%. there's example of in original answer below.

the reason original answer isn't entirely applicable because setx isn't destructive once thought. danger times when users want append directory path, they'll setx /m path "%path%;new dir"; , is destructive. because %path% expanded before setx writes value, directories in path expanded prematurely.

the following method safer:

set "env=hklm\system\currentcontrolset\control\session manager\environment"  /f "tokens=2*" %%i in (     'reg query "%env%" /v path ^| findstr /i "\<path\>"' ) setx /m path "%%j;new directory" 

but wasn't op asked, , apologize knee-jerk answer.

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original answer: setx destructive , shouldn't used way. when setx path you're converting registry value data type reg_expand_sz reg_sz. this, dynamic environment variables stored in %path% converted flat, absolute paths. use path command append directories %path% temporarily, , reg add permanently. (as side note, there's dpath, temporarily adds directory path, can used type command. scroll 2/3 way down this page more info on dpath.)

here's utility script wrote add directories %path% in less destructive manner. avoid adding same directory %path% more once, regardless of how it's formatted (e.g. trailing backslash, relative paths, environment variables, or other permutation).

@echo off setlocal enabledelayedexpansion  if not exist "%~1" goto usage  %%i in ("%~1") pushd "%%~i" 2>nul && (set "new=!cd!" && popd) || goto usage %%i in ("%path:;=";"%") pushd "%%~i" 2>nul && (     rem // delaying expansion of !new! prevents parentheses breaking things     if /i "!new!"=="!cd!" (         echo !new! exists in %%path%%         goto :eof     )     popd )  call :append_path "%new%"  goto :eof  :usage echo usage: %~nx0 "dir" goto :eof  :append_path <val> set "env=hklm\system\currentcontrolset\control\session manager\environment" /f "tokens=2*" %%i in ('reg query "%env%" /v path ^| findstr /i "\<path\>"') (      rem // make addition persistent through reboots     reg add "%env%" /f /v path /t reg_expand_sz /d "%%j;%~1"      rem // apply change current process     %%a in ("%%j;%~1") path %%~a )  rem // use setx set temporary throwaway value trigger wm_settingchange rem // applies change new console windows without requiring reboot (setx /m foo bar & reg delete "%env%" /f /v foo) >nul 2>nul  color 4e echo warning: %%path%% has changed.  reopen console inherit changes.  goto :eof