Related Resources from the NT/2K/XP/K3 Command Library

Go straight to !GuardNotes. (updated 2004-10-16)

Description

Displays, sets, or removes cmd.exe environment variables.

Syntax

Parameters and Switches

Examples, Notes and Instructions

Type SET without parameters to display the current environment variables.

If Command Extensions are enabled SET changes as follows:

SET command invoked with just a variable name, no equal sign or value will display the value of all variables whose prefix matches the name given to the SET command. For example:

    SET P

would display all variables that begin with the letter 'P'

SET command will set the ERRORLEVEL to 1 if the variable name is not found in the current environment.


SET command will not allow an equal sign to be part of the name of a variable.
 

SET command will allow an equal sign (=) in the value of an environment variable in any position other than the first character.

A new switch is added to the SET command:

SET command will not allow an equal sign to be part of the name of a variable.

Two new switches have been added to the SET command:

    SET /A expression

    SET /P variable=[promptString]

The /A switch specifies that the string to the right of the equal sign is a numerical expression that is evaluated. The expression evaluator is pretty simple and supports the following operations, in decreasing order of precedence:

If you use any of the logical or modulus operators, you will need to enclose the expression string in quotes. Any non-numeric strings in the expression are treated as environment variable names whose values are converted to numbers before using them. If an environment variable name is specified but is not defined in the current environment, then a value of zero is used.  This allows you to do arithmetic with environment variable values without having to type all those % signs to get their values.

If SET /A is executed from the command line outside of a command script, then it displays the final value of the expression. The assignment operator requires an environment variable name to the left of the assignment operator. Numeric values are decimal numbers, unless prefixed by 0x for hexiadecimal numbers, 0b for binary numbers and 0 for octals numbers. So 0x12 is the same as 0b10010 18 is the same as 022.  Please note that the octal notation can be confusing: 08 and 09 are not valid numbers because 8 and 9 are not valid octal digits.

The /P switch allows you to set the value of a variable to a line of input entered by the user. Displays the specified promptString before reading the line of input. The promptString can be empty.

Environment variable substitution has been enhanced as follows:

    %PATH:str1=str2%

would expand the PATH environment variable, substituting each occurrence of "str1" in the expanded result with "str2". "str2" can be the empty string to effectively delete all occurrences of "str1" from the expanded output. "str1" can begin with an asterisk, in which case it will match everything from the beginning of the expanded output to the first occurrence of the remaining portion of str1.

May also specify substrings for an expansion.

    %PATH:~10,5%

would expand the PATH environment variable, and then use only the 5 characters that begin at the 11th (offset 10) character of the expanded result.   If the length is not specified, then it defaults to the remainder of the variable value. If either number (offset or length) is negative, then the number used is the length of the environment variable value added to the offset or length specified.

    %PATH:~-10%

would extract the last 10 characters of the PATH variable.

    %PATH:~0,-2%

would extract all but the last 2 characters of the PATH variable.

Finally, support for delayed environment variable expansion has been added. This support is always disabled by default, but may be enabled/disabled via the /V command line switch to CMD.EXE. See CMD /?

Delayed environment variable expansion is useful for getting around the limitations of the current expansion which happens when a line of text is read, not when it is executed. The following example
demonstrates the problem with immediate variable expansion:

    SET VAR=before
    IF "%VAR%" == "before" (
        SET VAR=after;
        IF "%VAR%" == "after" @ECHO If you see this, it worked
    )

would never display the message, since the %VAR% in BOTH IF statements is substituted when the first IF statement is read, since it logically includes the body of the IF, which is a compound statement. So the IF inside the compound statement is really comparing "before" with "after" which will never be equal. Similarly, the following example will not work as expected:

    SET LIST=
    FOR %i IN (*) DO SET LIST=%LIST% %i
    ECHO %LIST%

in that it will NOT build up a list of files in the current directory, but instead will just set the LIST variable to the last file found.  Again, this is because the %LIST% is expanded just once when the
FOR statement is read, and at that time the LIST variable is empty.
So the actual FOR loop we are executing is:

    FOR %i IN (*) DO SET LIST= %i

which just keeps setting LIST to the last file found.

Delayed environment variable expansion allows you to use a different character (the exclamation mark) to expand environment variables at execution time. If delayed variable expansion is enabled, the above examples could be written as follows to work as intended:

    SET VAR=before
    IF "%VAR%" == "before" (
        SET VAR=after
        IF "!VAR!" == "after" @ECHO If you see this, it worked
    )

    SET LIST=
    FOR %i IN (*) DO SET LIST=!LIST! %i
    ECHO %LIST%

If Command Extensions are enabled, then there are several dynamic environment variables that can be expanded but which don't show up in the list of variables displayed by SET. These variable values are
computed dynamically each time the value of the variable is expanded.  If the user explicitly defines a variable with one of these names, then that definition will override the dynamic one described below:

GuardNotes

Maximum numeric values for SET /A

SET /A can work directly with numbers from -2,147,483,647 up to +2,147,483,647.  This allows for a wide variety of mathematical calculations using only the builtin command set.  The table below can be used a reference (numbers are always rounded down to the nearest whole integer when calculating).

In each row, starting with the value in green, you can successfully calculate any of the values to it's right in that row using only SET /A commands.

TIME	Seconds	Minutes	Hours	Days	Weeks	Months	Years
	2,147,483,647	35,791,394	596,523	24,855	3,550	814	67
		2,147,483,647	35,791,394	1,491,308	213,044	49,029	4,085
SIZE	Bits	Bytes	Kilobytes	Megabytes	Gigabytes	GB (1000MB)	Terabytes
	2,147,483,647	268,435,455	262,143	255	0	0	0
		2,147,483,647	2,097,151	2,047	1	2	0
			2,147,483,647	2,097,151	2,047	2,097	1
				2,147,483,647	2,097,151	2,147,483	2,047
DISTANCE (US)	Inches	Feet	Yards	Miles
	2,147,483,647	178,956,970	59,652,323	33,893
		2,147,483,647	715,827,882	406,720
DISTANCE (Metric)	millimeters	centimeters	meters	kilometers
	2,147,483,647	214,748,364	2,147,483	2,147
		2,147,483,647	21,474,836	21,474
			2,147,483,647	2,147,483
MONEY (US)	Pennies	Nickels	Dimes	Quarters	Dollars	$1000	$1M
	2,147,483,647	429,496,729	214,748,364	85,899,345	21,474,836	21,474	21
	Dollars	$Hundreds	$Thousands	$Millions	$Billions	$Trillions	$Quadrillions
	2,147,483,647	21,474,836	2,147,483	2,147	2	0
		2,147,483,647	214,748,364	214,748	214	0
			2,147,483,647	2,147,483	2,147	2
				2,147,483,647	2,147,483	2,147	2