Environment Variables

Environment variables store system and user configuration values that Windows and applications use to locate resources, configure behavior, and pass information between processes.

1. Overview#

Environment variables are name-value pairs maintained by the operating system and available to all running processes. They serve as a universal configuration mechanism, providing paths to system directories, user profile locations, processor information, and custom application settings.

Windows uses three scopes for environment variables:

System - apply to all users and services; stored in the registry
User - specific to the logged-in user; stored in the registry
Process - temporary, exist only for the lifetime of the current process and its children

2. Scope and Precedence#

When a process starts, it inherits a merged set of environment variables. If the same variable name exists in multiple scopes, the effective value follows this precedence (highest to lowest):

Process - set at runtime; overrides everything
User - set per user account
System - machine-wide defaults

Note: The PATH variable is special. System and User PATH values are concatenated (system first, then user), not overridden.

Registry Locations#

Scope	Registry Path
System	`HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Environment`
User	`HKCU:\Environment`

Changes to registry-based variables require a new process or a logoff/restart to take effect for existing processes. You can broadcast a WM_SETTINGCHANGE message to notify applications of the change.

3. Viewing Variables#

PowerShell#

# List all environment variables
Get-ChildItem Env:

# Get a specific variable
$env:APPDATA
$env:PATH

# Filter variables by pattern
Get-ChildItem Env: | Where-Object { $_.Name -like "*PROGRAM*" }

# View system vs user PATH separately
[Environment]::GetEnvironmentVariable("PATH", "Machine")
[Environment]::GetEnvironmentVariable("PATH", "User")

Command Prompt (CMD)#

:: List all environment variables
set

:: Show a specific variable
echo %APPDATA%

:: Show PATH
echo %PATH%

GUI#

Press Win + R, type sysdm.cpl, press Enter
Go to the Advanced tab
Click Environment Variables

4. Setting and Modifying Variables#

PowerShell#

# Set a process-scoped variable (temporary, current session only)
$env:MY_VAR = "value"

# Set a user-scoped variable (persistent)
[Environment]::SetEnvironmentVariable("MY_VAR", "value", "User")

# Set a system-scoped variable (persistent, requires admin)
[Environment]::SetEnvironmentVariable("MY_VAR", "value", "Machine")

# Remove a variable (set to null)
[Environment]::SetEnvironmentVariable("MY_VAR", $null, "User")

Command Prompt (CMD)#

:: Set a process-scoped variable (current session only)
set MY_VAR=value

:: Set a persistent user variable
setx MY_VAR "value"

:: Set a persistent system variable (requires admin)
setx MY_VAR "value" /M

:: Remove a variable
set MY_VAR=

Note: setx has a 1024-character limit for variable values. For longer values (especially PATH), use PowerShell or the GUI.

Registry (Direct)#

# Set a system variable via registry
Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Environment" `
    -Name "MY_VAR" -Value "value"

# Set a user variable via registry
Set-ItemProperty -Path "HKCU:\Environment" -Name "MY_VAR" -Value "value"

Broadcast Change Notification#

After modifying registry-based variables, notify running applications:

# Send WM_SETTINGCHANGE to notify applications
Add-Type -Namespace Win32 -Name NativeMethods -MemberDefinition @"
[DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)]
public static extern IntPtr SendMessageTimeout(
    IntPtr hWnd, uint Msg, UIntPtr wParam, string lParam,
    uint fuFlags, uint uTimeout, out UIntPtr lpdwResult);
"@
$result = [UIntPtr]::Zero
[Win32.NativeMethods]::SendMessageTimeout(
    [IntPtr]0xFFFF, 0x001A, [UIntPtr]::Zero, "Environment",
    0x0002, 5000, [ref]$result) | Out-Null

5. PATH Management#

The PATH variable tells Windows where to find executable files. It is a semicolon-separated list of directory paths.

View PATH Entries#

# List PATH entries, one per line
$env:PATH -split ";"

# View system PATH only
([Environment]::GetEnvironmentVariable("PATH", "Machine")) -split ";"

# View user PATH only
([Environment]::GetEnvironmentVariable("PATH", "User")) -split ";"

Add to PATH#

# Add to user PATH (persistent)
$currentPath = [Environment]::GetEnvironmentVariable("PATH", "User")
$newPath = "$currentPath;C:\MyTools"
[Environment]::SetEnvironmentVariable("PATH", $newPath, "User")

# Add to system PATH (persistent, requires admin)
$currentPath = [Environment]::GetEnvironmentVariable("PATH", "Machine")
$newPath = "$currentPath;C:\MyTools"
[Environment]::SetEnvironmentVariable("PATH", $newPath, "Machine")

# Add to current session only
$env:PATH += ";C:\MyTools"

Remove from PATH#

# Remove a directory from user PATH
$currentPath = [Environment]::GetEnvironmentVariable("PATH", "User")
$newPath = ($currentPath -split ";" | Where-Object { $_ -ne "C:\MyTools" }) -join ";"
[Environment]::SetEnvironmentVariable("PATH", $newPath, "User")

Clean Up Duplicate Entries#

$currentPath = [Environment]::GetEnvironmentVariable("PATH", "User")
$cleanPath = (($currentPath -split ";") | Select-Object -Unique | Where-Object { $_ -ne "" }) -join ";"
[Environment]::SetEnvironmentVariable("PATH", $cleanPath, "User")

6. Common Variables Reference#

System Directories#

Variable	Typical Value	Description
`%ALLUSERSPROFILE%`	`C:\ProgramData`	Common application data for all users
`%PROGRAMDATA%`	`C:\ProgramData`	Same as ALLUSERSPROFILE
`%PROGRAMFILES%`	`C:\Program Files`	64-bit program installation directory
`%PROGRAMFILES(X86)%`	`C:\Program Files (x86)`	32-bit program installation directory
`%ProgramW6432%`	`C:\Program Files`	64-bit program files (even from 32-bit process)
`%COMMONPROGRAMFILES%`	`C:\Program Files\Common Files`	Shared program components
`%COMMONPROGRAMFILES(x86)%`	`C:\Program Files (x86)\Common Files`	Shared 32-bit program components
`%SystemDrive%`	`C:`	Drive containing the Windows directory
`%SystemRoot%`	`C:\Windows`	Windows installation directory
`%WINDIR%`	`C:\Windows`	Same as SystemRoot
`%COMSPEC%`	`C:\Windows\System32\cmd.exe`	Path to the command interpreter
`%DriverData%`	`C:\Windows\System32\Drivers\DriverData`	Driver data directory

User Directories#

Variable	Typical Value	Description
`%APPDATA%`	`C:\Users\<username>\AppData\Roaming`	Roaming application data
`%LOCALAPPDATA%`	`C:\Users\<username>\AppData\Local`	Local application data
`%USERPROFILE%`	`C:\Users\<username>`	Current user's profile directory
`%HOMEDRIVE%`	`C:`	Drive letter of user's home directory
`%HOMEPATH%`	`\Users\<username>`	Path portion of user's home directory
`%TEMP%` / `%TMP%`	`C:\Users\<username>\AppData\Local\Temp`	Temporary file directory
`%USERNAME%`	`<username>`	Current user's login name
`%PUBLIC%`	`C:\Users\Public`	Public user profile
`%OneDrive%`	`C:\Users\<username>\OneDrive`	OneDrive sync folder

System Information#

Variable	Typical Value	Description
`%COMPUTERNAME%`	`<hostname>`	Machine hostname
`%USERDOMAIN%`	`<domain>`	Domain of the current user
`%USERDOMAIN_ROAMINGPROFILE%`	`<domain>`	Domain associated with roaming profile
`%LOGONSERVER%`	`\\<server>`	Domain controller that authenticated the user
`%OS%`	`Windows_NT`	Operating system identifier
`%PROCESSOR_IDENTIFIER%`	(varies)	Processor description string
`%PROCESSOR_LEVEL%`	(varies)	Processor family level
`%PROCESSOR_REVISION%`	(varies)	Processor revision number
`%NUMBER_OF_PROCESSORS%`	(varies)	Count of logical processors

Shell and Path#

Variable	Typical Value	Description
`%PATH%`	(semicolon-separated dirs)	Executable search path
`%PathExt%`	`.com;.exe;.bat;.cmd;.vbs;.vbe;.js;.jse;.wsf;.wsh;.msc`	File extensions treated as executable
`%PROMPT%`	`$P$G`	CMD prompt format string
`%PSModulePath%`	(semicolon-separated dirs)	PowerShell module search path

CMD-Only Dynamic Variables#

These variables are only available in Command Prompt sessions and are evaluated dynamically:

Variable	Description
`%CD%`	Current working directory
`%DATE%`	Current date
`%TIME%`	Current time
`%RANDOM%`	Random number (0 through 32767)
`%ERRORLEVEL%`	Exit code of the previous command
`%CMDCMDLINE%`	Command line used to launch the CMD session
`%CMDEXTVERSION%`	Command processor extensions version number

7. Using Variables in Scripts#

In PowerShell#

# Access environment variables
$appData = $env:APPDATA
$home = $env:USERPROFILE

# Use in paths
$logFile = Join-Path $env:TEMP "myapp.log"

# Expand variables in strings (double quotes only)
Write-Host "User profile is at $env:USERPROFILE"

# Access via the Env: drive
Get-Item Env:COMPUTERNAME
Set-Item Env:MY_VAR -Value "test"
Remove-Item Env:MY_VAR

In CMD Batch Files#

:: Access variables with percent signs
echo %USERNAME% on %COMPUTERNAME%

:: Set and use in the same script
set LOGDIR=%TEMP%\logs
mkdir %LOGDIR%

:: Delayed expansion (inside loops)
setlocal enabledelayedexpansion
for /L %%i in (1,1,5) do (
    set COUNT=%%i
    echo !COUNT!
)
endlocal

In Application Configuration#

Many applications and frameworks use environment variables for configuration:

# Set Java home
[Environment]::SetEnvironmentVariable("JAVA_HOME", "C:\Program Files\Java\jdk-21", "Machine")

# Set Node.js options
[Environment]::SetEnvironmentVariable("NODE_OPTIONS", "--max-old-space-size=4096", "User")

# Set proxy for development tools
[Environment]::SetEnvironmentVariable("HTTP_PROXY", "http://<proxy-host>:<port>", "User")
[Environment]::SetEnvironmentVariable("HTTPS_PROXY", "http://<proxy-host>:<port>", "User")

Troubleshooting#

Issue	Cause	Solution
Variable change not visible in open terminals	Existing processes have stale environment	Open a new terminal; or broadcast `WM_SETTINGCHANGE`
`setx` truncates PATH	PATH exceeds 1024-character `setx` limit	Use PowerShell `[Environment]::SetEnvironmentVariable()` or the GUI instead
Application cannot find executable	Directory not in PATH	Add the directory to PATH and open a new terminal
User variable overrides system variable	Same name exists in both scopes	Rename or remove one; remember PATH is concatenated, not overridden
`%VARIABLE%` prints literally in CMD	Variable does not exist	Verify spelling and scope; use `set` to list all variables
`$env:VAR` is empty in PowerShell	Variable not set for current scope	Check with `[Environment]::GetEnvironmentVariable("VAR", "Machine")` and `"User"` separately
Changes lost after reboot	Variable was set with `$env:` or `set` (process-scoped only)	Use `setx`, `[Environment]::SetEnvironmentVariable()`, or the GUI for persistence

Environment Variables

1. Overview#

2. Scope and Precedence#

Registry Locations#

3. Viewing Variables#

PowerShell#

Command Prompt (CMD)#

GUI#

4. Setting and Modifying Variables#

PowerShell#

Command Prompt (CMD)#

Registry (Direct)#

Broadcast Change Notification#

5. PATH Management#

View PATH Entries#

Add to PATH#

Remove from PATH#

Clean Up Duplicate Entries#

6. Common Variables Reference#

System Directories#

User Directories#

System Information#

Shell and Path#

CMD-Only Dynamic Variables#

7. Using Variables in Scripts#

In PowerShell#

In CMD Batch Files#

In Application Configuration#

Troubleshooting#

See Also#

Sources#