Environment Variables in Windows XP

Environment variables are strings that contain information such as drive, path, or file name. They control the behavior of various programs. For example, the TEMP environment variable specifies the location in which programs place temporary files.

Table I. Some more common predefined environment variables

Variable	Typical value (May vary, depending on system)
%ALLUSERSPROFILE%	C:\Documents and Settings\All Users
%APPDATA%	C:\Documents and Settings\{username}\Application Data
%COMPUTERNAME%	{computername}
%COMSPEC%	C:\Windows\System32\cmd.exe
%HOMEDRIVE%	C:
%HOMEPATH%	\Documents and Settings\{username}
%PATH%	C:\Windows\System32\;C:\Windows\;C:\Windows\System32\Wbem
%PATHEXT%	.COM; .EXE; .BAT; .CMD; .VBS; .VBE; .JS ; .WSF; .WSH
%PROGRAMFILES%	Directory containing program files, usually C:\Program Files
%PROMPT%	Code for current command prompt format. Code is usually $P$G
%SYSTEMDRIVE%	The drive containing the Windows XP root directory, usually C:
%SYSTEMROOT%	The Windows XP root directory, usually C:\Windows
%TEMP% and %TMP%	C:\DOCUME~1\{username}\LOCALS~1\Temp
%USERNAME%	{username}
%USERPROFILE%	C:\Documents and Settings\{username}
%WINDIR%	C:\Windows

The so-called predefined variables are generally unchanged during a login session but there are also some dynamic variables whose value may change. Some of these are listed in the next table.

Table II. Some dynamic environment variables

Variable	Value
%DATE%	Current date in the format determined by the Date command
%TIME%	Current time in the format determined by the Time command
%CD%	Current directory with its full path
%ERRORLEVEL%	Number defining exit status of a previous command or program
%RANDOM%	Random number between 0 and 32767