A. You can use environment variables to gain information about a system. For a complete list of environment variables available in Windows, see the following table:
Table 1: Environment Variables
| ALLUSERSPROFILE |
Local returns the location of the All Users Profile. |
| APPDATA |
Local returns the location where applications store data by
default. |
| CD |
Local returns the current directory string. |
| CMDCMDLINE |
Local returns the exact command line used to start the
current cmd.exe. |
| CMDEXTVERSION |
System returns the version number of the current Command
Processor Extensions. |
| COMPUTERNAME |
System returns the name of the computer. |
| COMSPEC |
System returns the exact path to the command shell
executable. |
| DATE |
System returns the current date. This variable uses the same format as the date /t command. Cmd.exe generates this variable. For more information about the date command, see the Date command. |
| ERRORLEVEL |
System returns the error code of the most recently used
command. A non-0 value usually indicates an error. |
| HOMEDRIVE |
System returns which local workstation drive letter is
connected to the user's home directory. This variable is set based on the value of the home directory. The user's home directory is specified in Local Users and Groups. |
| HOMEPATH |
System returns the full path of the user's home directory.
This variable is set based on the value of the home directory. The user's home directory is specified in Local Users and Groups. |
| HOMESHARE |
System returns the network path to the user's shared home
directory. This variable is set based on the value of the home directory. The user's home directory is specified in Local Users and Groups. |
| LOGONSEVER |
Local returns the name of the domain controller that
validated the current logon session. |
| NUMBER_OF_PROCESSORS |
System specifies the number of processors installed on the
computer. |
| OS |
System returns the OS name. Windows XP and Windows 2000 display the OS as Windows_NT. |
| PATH |
System specifies the search path for executable files. |
| PATHEXT |
System returns a list of the file extensions that the
OS considers to be executable. |
| PROCESSOR_ARCHITECTURE |
System returns the processor's chip architecture.
Values: x86, IA64. |
| PROCESSOR_IDENTFIER |
System returns a description of the processor. |
| PROCESSOR_LEVEL |
System returns the model number of the computer's processor. |
| PROCESSOR_REVISION |
System returns the revision number of the processor. |
| PROMPT |
Local returns the command-prompt settings for the current
interpreter. Cmd.exe generates this variable. |
| RANDOM |
System returns a random decimal number between 0 and 32767. Cmd.exe generates this variable. |
| SYSTEMDRIVE |
System returns the drive containing the Windows root
directory (i.e., the system root). |
| SYSTEMROOT |
System returns the location of the Windows root directory.
|
| TEMP or TMP |
System and User return the default temporary directories
for applications that are available to users who are currently logged
on. Some applications require TEMP and others require TMP. |
| TIME |
System returns the current time. This variable uses the same format as the time /t command. Cmd.exe generates this variable. For more information about the time command, see the Time command. |
| USERDOMAIN |
Local returns the name of the domain that contains the
user's account. |
| USERNAME |
Local returns the name of the user currently logged
on. |
| USERPROFILE |
Local returns the location of the profile for the current
user. |
| WINDIR |
System returns the location of the OS directory |
To access these environment variables, you must place a percentage symbol (%) before and after the variable. For example,
echo %PROCESSOR_ARCHITECTURE%
x86
will display the processor type (but still won't display Intel's ia64 platform).
Some environment variables are available only in later OSs (e.g., %RANDOM% is not available in Windows NT 4.0).