Networking / Beginners

Networking Environment variables

The command shell makes several environment variables available to commands. Environment variables all begin and end with percent signs. You can use an environment variable anywhere in a command. For example,

C:\>echo %OS% running on a %PROCESSOR_IDENTIFIER%

displays a line such as this:

Windows_NT running on an x86 Family 15 Model 2 Stepping 8, GenuineIntel

Interestingly, Windows NT, Windows 2000 Server, Windows Server 2003, and Windows Server 2008 all display "Windows_NT" for the operating system name.

If the environment variable represents a path, you may need to enclose it in quotation marks, like this:

C:\>dir "%HOMEPATH%"

This command displays the contents of the user's home directory. The quotation marks are required here because the environme>nt variable expands to a pathname that may include spaces, and the command shell requires that long filenames that include spaces must be enclosed in quotation marks.

Table-1 lists the environment variables that are available to you and your commands.

%ALLUSERSPROFILE%The location of the All Users profile
%APPDATA%The path where applications store data by default
%CD%The path to the current directory
%CMDCMDLINE%The command line that was used to start the command shell
%CMDEXTVERSION%The version number of the command shell
%COMPUTERNAME%The computer's name
%COMSPEC%The path to the command shell executable (cmd.exe)
%DATE%The current date in the format generated by the date /t command
%ERRORLEVEL%The error returned by the most recent command
%HOMEDRIVE%The drive letter of the user's home directory
%HOMEPATH%The path to the user's home directory
%HOMESHARE%The network path to the user's shared home directory
%LOGONSERVER%The name of the domain controller the user logged on to
%NUMBER_OF_PROCESSORS%The number of processors on the computer
%OS%The name of the operating system
%PATH%The current search path
"%PATHEXT%"A list of the extensions the operating system treats as executable files
%PROCESSOR_ARCHITECTURE%The chip architecture of the processor
%PROCESSOR_IDENTIFIER%A description of the processor
%PROCESSOR_REVISION%The revision level of the processor
%PROMPT%The current prompt string
%RANDOM%A random number between 1 and 32,767
%SYSTEMDRIVE%The drive containing the operating system
%SYSTEMROOT%The path to the operating system
%TEMP%The path to a temporary folder for temporary files
%TMP%Same as %TEMP%
%TIME%The time in the format produced by the time /t command
%USERDOMAIN%The name of the user's domain
%USERNAME%The user's account name
%USERPROFILE%The path to the user's profile
%WINDIR%The path to the operating system directory

Batch files

A batch file is simply a text file that contains one or more commands. Batch files are given the extension .bat and can be run from a command prompt as if they were commands or programs. You can also run a batch file from the Start menu by choosing Start → Run, typing the name of the batch file, and clicking OK.

As a network administrator, you'll find plenty of uses for batch files. Most of them won't be very complicated. For example, here are some examples of very simple batch files:

  • Used a one-line file to copy the entire contents of an important shared network drive to a user's computer every night at 10 p.m. The user had just purchased a new Dell computer with a 100GB drive, and the server had only a 20GB drive. The user wanted a quick-and-dirty backup solution that would complement the regular tape backups that ran every night.
  • Used a pair of short batch files to stop and then restart Exchange server before and after nightly backups for backup software that didn't have an Exchange plug-in that could back up the mail store while it was open.
  • If frequently need to work with several related folders at once, create a short batch file that opens Explorer windows for each of the folders. (You can open an Explorer window from a batch file simply by typing the path to the folder that you want to open as a command.) Then, place the batch file on my desktop so I can get to it quickly.

You can also use batch files to create logon scripts that are executed whenever a user logs on. Microsoft keeps trying to get users to use profiles instead of logon scripts, but many networks still use logon scripts.

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