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The PATH Environment Variable

The

path

to a file is basically its address on the computer. It tells programs how to find a file. It is the drive plus any directories and sub-directories where the file is located. The %PATH% environment variable specifies the command search path. Typically, this is a group of directories where executable files that are repeatedly used are to be found. Examples of the default values are listed in the first table above; in this case, they are the Windows directory and two of its important system sub-directories. To see what is in the PATH variable on a computer, open a command window and enter "echo %PATH%".

The PATH variable is not immutable and programs like Norton SystemWorks will stick themselves into PATH when they are installed. The PC user can also modify the contents using methods discussed

further on. Adding directories to PATH can be very useful if you use scripts or the command line for system maintenance. For example, it can be convenient to put the directory where you keep backups into the PATH variable. It can also be useful to modify PATH if you put programs in a directory different from the usual one.

In the command line and in batch files, PATH can be modified by the commandpath = dir1;dir2;dir3This command will create a PATH environment variable consisting of the three directories

dir1,

dir2, and

dir3. Note that the directory names are separated by a semicolon in the command statement. (An alternate form omits the "equals" sign.) This command will

replace

any previous directories that were in the PATH variable. To

add

a directory "newdir" to the current path use the statementpath = %PATH%;newdir

It is essential to remember that any changes that are made in a command window only endure until the window is closed. For permanent changes, use the method discussed in

another section. It is also possible to use the command-line executable

setx.exe

that is contained in the

Windows XP Service Pack 2 Support Tools.

Any file that is in a directory listed in the PATH variable can be found or opened by direct reference to the name of the file without having to specify the drive and directories where it is located. This is very handy in scripting and in other ways. For instance, the name of an executable file that is in a directory listed in the PATH variable can be entered into

Start-Run

to open certain applications (more on this subject

here). An example is the executable file for the classic version of the game Solitaire that is generally in the system folder

C:\Windows\System32\.

The file is

sol.exe

and its full address with complete path is

C:\Windows\System32\sol.exe.

Normally this entire string would have to be used in order to reference the Solitaire game. Because its directory is listed in the PATH variable, however, it is sufficient to reference just the file name

sol.exe.

In fact, because of another environment variable PATHEXT discussed next, simply entering

sol

into

Start-Run

is sufficient to open the solitaire game.

The PATHEXT Variable

As is explained on

other pages, file extensions tell Windows what it is supposed to do with a file. Certain file extensions indicate that the file isexecutable; that is, the file opens a program or does something. The %PATHEXT% environment variable contains executable file extensions that do not have to be specified for any file in a directory given in the %PATH% variable. The extension .EXE is the most common. Thus the filenamesol.exe

need only be entered as

sol

in a command line. If files have the same name but different extensions, the operating system searches in the following order of precedence: .EXE, .COM, .BAT, and .CMD.

Adding or Editing Environment Variables

Existing variables can be edited or deleted and new ones can be added in several ways. For temporary changes, the command " Set" can be used in scripts or in a command window. An example is shown below:set temp=C:\tempHere, the %TEMP% directory has been changed from the default value. Note that the there must be no spaces on either side of the "equals" sign. Changes made with "Set" disappear when the command window is closed, thus rendering this method fairly uninteresting for the average PC user. A more useful application of "Set" is to list the environment variables. Open a command window and enter "set" to see what the variables are on your system. Those who wish can consult this

Microsoft article

for more details about "Set".

A more permanent way to manage environment variables is provided in the System Properties dialog box. Open

Control Panel-Performance and Maintenance-System

(or right-click on

My Computer

and choose "Properties"). In the box that opens, click the "Advanced" tab to obtain the dialog box shown below. Next, click the button "Environment Variables".

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