HowTo: Set an Environment Variable in Windows — Command Line and Registry

Environment variables are not often seen directly when using Windows. However there are cases, especially when using the command line, that setting and updating environment variables is a necessity. In this series we talk about the various approaches we can take to set them. In this article we look at how to interface with environment variables using the Command Prompt and Windows PowerShell. We also note where in the registry the environment variables are set, if you needed to access them in such a fashion.

Print environment variables

You can use environment variables in the values of other environment variables. It is then helpful to be able to see what environment variables are set already. This is how you do it:

Command Prompt

List all environment variables

Command Prompt — C:\>

Output

Print a particular environment variable:

Command Prompt — C:\>

Output

Windows PowerShell

List all environment variables

Windows PowerShell — PS C:\>

Output

Print a particular environment variable:

Windows PowerShell — PS C:\>

Output

Set Environment Variables

To set persistent environment variables at the command line, we will use setx.exe . It became part of Windows as of Vista/Windows Server 2008. Prior to that, it was part of the Windows Resource Kit. If you need the Windows Resource Kit, see Resources at the bottom of the page.

setx.exe does not set the environment variable in the current command prompt, but it will be available in subsequent command prompts.

User Variables

Command Prompt — C:\>

Open a new command prompt.

Command Prompt — C:\>

Output

System Variables

To edit the system variables, you’ll need an administrative command prompt. See HowTo: Open an Administrator Command Prompt in Windows to see how.

Command Prompt — C:\>

Registry

The location of the user variables in the registry is: HKEY_CURRENT_USER\ Environment . The location of the system variables in the registry is: HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Control\ Session Manager\ Environment .

When setting environment variables through the registry, they will not recognized immediately. One option is to log out and back in again. However, we can avoid logging out if we send a WM_SETTINGCHANGE message, which is just another line when doing this programatically, however if doing this on the command line it is not as straightforward.

One way is to get this message issued is to open the environment variables in the GUI, like we do in HowTo: Set an Environment Variable in Windows — GUI; we do not need to change anything, just open the Environment Variables window where we can see the environment variables, then hit OK .

Another way to get the message issued is to use setx , this allows everything to be done on the command line, however requires setting at least one environment variable with setx .

Printing Environment Variables

With Windows XP, the reg tool allows for accessing the registry from the command line. We can use this to look at the environment variables. This will work the same way in the command prompt or in powershell. This technique will also show the unexpanded environment variables, unlike the approaches shown for the command prompt and for powershell.

set (environment variable)

Displays, sets, or removes cmd.exe environment variables. If used without parameters, set displays the current environment variable settings.

This command requires command extensions, which are enabled by default.

The set command can also run from the Windows Recovery Console, using different parameters. For more information, see Windows Recovery Environment (WinRE).

Syntax

Parameters

Parameter	Description
Specifies the environment variable to set or modify.
Specifies the string to associate with the specified environment variable.
/p	Sets the value of to a line of input entered by the user.
Specifies a message to prompt the user for input. This parameter must be used with the /p parameter.
/a	Sets to a numerical expression that is evaluated.
Specifies a numerical expression.
/?	Displays help at the command prompt.

Remarks

If command extensions are enabled (the default) and you run set with a value, it displays all of the variables that begin with that value.

The characters , > , | , & , and ^ are special command shell characters, and they must be preceded by the escape character ( ^ ) or enclosed in quotation marks when used in (for example, «StringContaining&Symbol»). If you use quotation marks to enclose a string that contains one of the special characters, the quotation marks are set as part of the environment variable value.

Use environment variables to control the behavior of some batch files and programs and to control the way Windows and the MS-DOS subsystem appears and works. The set command is often used in the Autoexec.nt file to set environment variables.

If you use the set command without any parameters, the current environment settings are displayed. These settings usually include the COMSPEC and PATH environment variables, which are used to help find programs on disk. Two other environment variables used by Windows are PROMPT and DIRCMD.

If you specify values for and , the specified value is added to the environment and is associated with that variable. If the variable already exists in the environment, the new string value replaces the old string value.

If you specify only a variable and an equal sign (without ) for the set command, the value associated with the variable is cleared (as if the variable is not there).

If you use the /a parameter, the following operators are supported, in descending order of precedence:

Operator	Operation performed
( )	Grouping
! —	Unary
* / %	Arithmetic
+ —	Arithmetic
>	Logical shift
&	Bitwise AND
^	Bitwise exclusive OR
= *= /= %= += -= &= ^=	= >=
,	Expression separator

If you use logical ( && or || ) or modulus (%) operators, enclose the expression string in quotation marks. Any non-numeric strings in the expression are considered environment variable names, and their values are converted to numbers before they are processed. If you specify an environment variable name that is not defined in the current environment, a value of zero is allotted, which allows you to perform arithmetic with environment variable values without using the % to retrieve a value.

If you run set /a from the command line outside of a command script, it displays the final value of the expression.

Numeric values are decimal numbers unless prefixed by 0Г— for hexadecimal numbers or 0 for octal numbers. Therefore, 0Г—12 is the same as 18, which is the same as 022.

Delayed environment variable expansion support is disabled by default, but you can enable or disable it by using cmd /v.

When creating batch files, you can use set to create variables, and then use them in the same way that you would use the numbered variables %0 through %9. You can also use the variables %0 through %9 as input for set.

If you call a variable value from a batch file, enclose the value with percent signs (%). For example, if your batch program creates an environment variable named BAUD, you can use the string associated with BAUD as a replaceable parameter by typing %baud% at the command prompt.

Examples

To set the value TEST^1 for the environment variable named testVar , type:

The set command assigns everything that follows the equal sign (=) to the value of the variable. Therefore, if you type set testVar=test^1 , you’ll get the following result, testVar=test^1 .

To set the value TEST&1 for the environment variable testVar , type:

To set an environment variable named INCLUDE so the string c:\directory is associated with it, type:

You can then use the string c:\directory in batch files by enclosing the name INCLUDE with percent signs (%). For example, you can use dir %include% in a batch file to display the contents of the directory associated with the INCLUDE environment variable. After this command is processed, the string c:\directory replaces %include%.

To use the set command in a batch program to add a new directory to the PATH environment variable, type:

To display a list of all of the environment variables that begin with the letter P, type:

Windows set environment variable from command line

Display, set, or remove CMD environment variables. Changes made with SET will remain only for the duration of the current CMD session.

Variable names are not case sensitive but the contents can be.

It is good practice to avoid using any delimiter characters (spaces, commas etc) in the variable name.

Delimiter characters can be used in the value if the complete assignment is surrounded with double quotes to prevent the delimiter being interpreted.

Any extra spaces around either the variable name or the string, will not be ignored, SET is not forgiving of extra spaces like many other scripting languages. So use SET alpha=beta , not SET alpha = beta

The first character of the name must not be numeric. It is a common practice to prefix variable names with either an undescore or a dollar sign _variable or $variable , these prefixes are not required but help to prevent any confusion with the standard built-in Windows Environment variables or any other other command strings.

The CMD shell will fail to read an environment variable if it contains more than 8,191 characters.

Display a variable:

In most contexts, surround the variable name with % ‘s and the variable’s value will be used
e.g. To display the value of the _department variable with the ECHO command:
ECHO %_department%

If the variable name is not found in the current environment then SET will set %ERRORLEVEL% to 1 .
This can be detected using IF ERRORLEVEL .

Including extra characters can be useful to show any white space:
ECHO [%_department% ]
ECHO «%_department% »

Type SET without parameters to display all the current environment variables.

Type SET with a variable name to display that variable
SET _department

The SET command invoked with a string (and no equal sign) will display a wildcard list of all matching variables

Display variables that begin with ‘P’:
SET p
Display variables that begin with an underscore
SET _

Set a variable:

Example of storing a text string:

C:\> SET _dept=Sales and Marketing
C:\> set _
_dept=Sales and Marketing

Set a variable that contains a redirection character, note the position of the quotes which are not saved:

SET «_dept=Sales & Marketing»

One variable can be based on another, but this is not dynamic
E.g.

C:\> set «xx=fish»
C:\> set «msg=%xx% chips»
C:\> set msg
msg=fish chips

C:\> set «xx=sausage»
C:\> set msg
msg=fish chips

C:\> set «msg=%xx% chips»
C:\> set msg
msg=sausage chips

Avoid starting variable names with a number, this will avoid the variable being mis-interpreted as a parameter
%123_myvar% %1 23_myvar

To display undocumented system variables:

Values with Spaces — using Double Quotes

Although it is advisable, there is no requirement to add quotation marks when assigning a value that includes spaces:

SET _variable=one two three

For special characters like & surround the entire expression with quotation marks.
The variable contents will not include the surrounding quotes:

n.b. if you only place quotation marks around the value, then those quotes will be stored:

Variable names with spaces

A variable can contain spaces and also the variable name itself can contain spaces, therefore the following assignment:
SET _var =MyText
will create a variable called «_var » — note the trailing space

Prompt for user input

The /P switch allows you to set a variable equal to a line of input entered by the user.
The Prompt string is displayed before the user input is read.

The Prompt string can be empty. The variable name can also be left empty but this is undocumented.

If the user does not enter anything (just presses return) then the variable will be unchanged and an errorlevel will be set to 1.

The CHOICE command is an alternative to SET /P (but CHOICE accepts only one character/keypress.)

Place the first line of a file into a variable:

Better still, to be sure there is no trailing space after the = place the expression in parentheses or quotes:
(SET _department=)
or
SET «_department=»

Arithmetic expressions (SET /a)

Placing expressions in «quotes» is optional for simple arithmetic but required for any expression using logical operators.

When refering to a variable in your expression, SET /A allows you to omit the %’s so _myvar instead of %_myvar%

Any SET /A calculation that returns a fractional result will be rounded down to the nearest whole integer.

The expression to be evaluated can include the following operators:
For the Modulus operator use (%) on the command line, or in a batch script it must be doubled up to (%%) as below.
This is to distinguish it from a FOR parameter.

If a variable name is specified as part of the expression, but is not defined in the current environment, then SET /a will use a value of 0.

SET /A arithmetic shift operators do not detect overflow which can cause problems for any non-trivial math, e.g. the bitwise invert often incorrectly reverses the + / — sign of the result.

See SET /a examples below and this forum thread for more.
also see SetX, VarSearch and VarSubstring for more on variable manipulation.

SET /A should work within the full range of 32 bit signed integer numbers (-2,147,483,648 through 2,147,483,647) but in practice for negative integers it will not go below -2,147,483,647

SET /A «_result=2+4»
(=6)

SET /A «_result=2 SET /A «_result=5 + _MyVar «

Multiple calculations can be performed in one line, by separating each calculation with commas, for example:

Set «_year=1999»
Set /a «_century=_year/100, _next=_century+1»

The numbers must all be within the range of 32 bit signed integer numbers (-2,147,483,648 through 2,147,483,647) to handle larger numbers use PowerShell or VBScript.

Leading Zero will specify Octal

Numeric values are decimal numbers, unless prefixed by
0x for hexadecimal numbers,
0 for octal numbers.

So 0x10 = 020 = 16 decimal

The octal notation can be confusing — all numeric values that start with zeros are treated as octal but 08 and 09 are not valid octal digits.
For example SET /a «_month=07 » will return the value 7, but SET /a «_month=09» will return an error.

Permanent changes

Changes made using the SET command are NOT permanent, they apply to the current CMD prompt only and remain only until the CMD window is closed.
To permanently change a variable at the command line use SetX
or with the GUI — Control Panel | System | Environment | System/User Variables

Changing a variable permanently with SetX will not affect any CMD prompt that is already open.
Only new CMD prompts will get the new setting.

You can of course use SetX in conjunction with SET to change both at the same time:

Set _Library=T:\Library\
SetX _Library T:\Library\ /m

Change the environment for other sessions

Neither SET nor SetX will affect other CMD sessions that are already running on the machine . This as a good thing, particularly on multi-user machines, your scripts won’t have to contend with a dynamically changing environment while they are running.

It is possible to add permanent environment variables to the registry ( HKCU\Environment ), but this is an undocumented (and likely unsupported) technique and still it will not take effect until the users next login.

System environment variables can be found in the registry here:
HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Environment

CALL SET

The CALL SET syntax allows a variable substring to be evaluated, the CALL page has more detail on this technique, in most cases a better approach is to use Setlocal EnableDelayedExpansion

Autoexec.bat

Any SET statement in c:\autoexec.bat will be parsed at boot time
Variables set in this way are not available to 32 bit gui programs — they won’t appear in the control panel.
They will appear at the CMD prompt.

If autoexec.bat CALLS any secondary batch files, the additional batch files will NOT be parsed at boot.
This behaviour can be useful on a dual boot PC.

Errorlevels

Errorlevel

If the variable was successfully changed	unchanged , typically this will be 0 but if a previous command set an errorlevel, that will be preserved (this is a bug).
SET No variable found or invalid name. SET _var=value when _var name starts with «/» and not enclosed in quotes. SET /P Empty response from user.	1
SET /A Unbalanced parentheses	1073750988
SET /A Missing operand	1073750989
SET /A Syntax error	1073750990
SET /A Invalid number	1073750991
SET /A Number larger than 32-bits	1073750992
SET /A Division by zero	1073750993

SET is an internal command.
If Command Extensions are disabled all SET commands are disabled other than simple assignments like: _variable=MyText

# I got my mind set on you
# I got my mind set on you. — Rudy Clark (James Ray/George Harrison)

Syntax — VarSubstring Extract part of a variable (substring).
Syntax — VarSearch Search & replace part of a variable.
Syntax — Environment Variables — List of default variables.
CALL — Evaluate environment variables.
ENDLOCAL — End localisation of environment changes, use to return values.
EXIT — Set a specific ERRORLEVEL.
PATH — Display or set a search path for executable files.
REG — Read or Set Registry values.
SETLOCAL — Begin localisation of environment variable changes.
SETX — Set an environment variable permanently.
WMIC ENVIRONMENT — Set environment variables through WMI.
Parameters — get a full or partial pathname from a command line variable.
StackOverflow — Storing a Newline in a variable.
Powershell: Set-Variable — Set a variable and a value (set/sv).
Powershell: Read-Host — Prompt for user input.
Equivalent bash command (Linux): env — Display, set, or remove environment variables.