Windows NT 4/Windows 2000 Syntax
|Note:||The parts of this text that are displayed in magenta are valid for Windows 2000 only|
Displays, sets, or removes cmd.exe environment variables.
|variable||Specifies the environment-variable name.|
|string||Specifies a series of characters to assign to the variable.|
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:
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.
However, SET command will allow an equal sign in the value of an environment variable in any position other than the first character.
One new switch has been added to the SET command in Windows NT 4, and another one in Windows 2000:
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:
|* / %||- arithmetic operators|
|+ -||- arithmetic operators|
|<< >>||- logical shift|
|&||- bitwise and|
|^||- bitwise exclusive or|
|¦||- bitwise or|
|= *= /= %= += -=
&= ^= ¦= <<= >>=
|,||- expression separator|
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 hexidecimal numbers, 0b for binary numbers and 0 for octals numbers. So 0x12 is the same as 0b10010 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:
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 begining of the expanded output to the first occurrence of the remaining portion of str1.
May also specify substrings for an expansion.
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.
would extract the last 10 characters of the PATH variable.
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=beforeif "%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% %iecho %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=beforeif "%VAR%" == "before" (set VAR=afterif "!VAR!" == "after" @echo If you see this, it worked)set LIST=for %i in (*) do set LIST=!LIST! %iecho %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:
|%CD%||-||expands to the current directory string.|
|%DATE%||-||expands to current date using same format as DATE command.|
|%TIME%||-||expands to current time using same format as TIME command.|
|%RANDOM%||-||expands to a random decimal number between 0 and 32767.|
|%ERRORLEVEL%||-||expands to the current ERRORLEVEL value.|
|%CMDEXTVERSION%||-||expands to the current Command Processor Extensions version number.|
|%CMDCMDLINE%||-||expands to the original command line that invoked the Command Processor.|
|Warning note:||A note on NT 4's SET /A switch from Walter Zackery in a message on alt.msdos.batch.nt:|
|"The SET /A command has a long list of problems. I wouldn't use it for much more than simple arithmetic, although even then it truncates all answers to integers."|
On the other hand, limited though it may seem, the SET command's math function can even be used for a complex task like calculating the date of Easter Day for any year.