cmd

cmd

Runs a new instance of the command-line shell.

Syntax

 cmd [/a  /u] [/q] [/d] [/e:on  /e:off] [/f:on  /f:off] [/v:on   /v:off] [ [/s] [/t:bf] [/c  /k]   command   ]

Options

None

Opens a new command shell.

command

Runs the specified command in the current command shell.

/c

Executes command and then exits the shell. (The remainder of the command following the /c switch is processed as a command line.)

/k

Executes command and continues running the shell. (The remainder of the command following the /k switch is processed as a command line.)

/s

If the first character after /c or /k is a quote and the /s switch is used, strips the leading and final closing quotes and retains any other quotes in the line as part of the command.

/q

Disables local echo.

/d

Disables running AutoRun commands, which are stored in the registry and executed by default whenever cmd is run. The registry locations are:

 HKLM\Software\Microsoft\Command Processor\AutoRun HKCU\Software\Microsoft\Command Processor\AutoRun

/a

Sets output to ANSI.

/u

Sets output to Unicode.

/t:bf

Specifies background and foreground colors using hexadecimal numeric codes of the color command (type color /? for a list of codes).

/e:[on off]

Enables or disables command-shell extensions (enabled by default), which extend the functionality of the following commands: del ( erase ), color , cd ( chdir ), md ( mdir ), prompt , pushd , popd , set , setlocal , endlocal , if , for , call , shift , goto , start , assoc , and ftype .

/f:[on off]

Enables or disables filename and directory name completion characters (disabled by default), which use Ctrl-D and Ctrl-F for directory and filename completion, respectively.

/v:[on off]

Disables delayed environment-variable expansion (disabled by default). If enabled, you can use the exclamation character ( ! ) to substitute the value of environment variables at runtime.

Examples

Turn autocompletion on:

  cmd /f:on

Change to the C:\Program Files directory using autocompletion:

  cd p

Then press Ctrl-D several times until "Program Files" appears, and then press Enter.

Discussion

Because understanding cmd is essential to running all other commands in this chapter, it's worth taking a deeper look at how it works.

Opening a Command Shell

To launch the command interpreter from the GUI:

Start All Programs Accessories Command Prompt

Start Run cmd OK

To start a new instance of the command interpreter from an existing instance:

Command interpreter cmd (opens a nested command shell in the same window)

Command interpreter start cmd (opens a new command shell)

Tip: to quit a nested shell, type exit .

Configuring a Command Shell

To configure the properties of a command prompt window, right-click on the titlebar of the window and select Properties. This opens a properties sheet with four tabs. The key settings here are:

Options: Switches the command interpreter between full screen and a window (you can switch between them using Alt-Enter), enables QuickEdit (which lets you cut and paste using a mouse instead of the tedious Edit menu), enables Insert mode (which lets you insert text at the present cursor position instead of overwriting previous text there), and configures the number of commands that can be remembered in the command-history buffer (you access previously typed commands by using the up and down arrow keys).
Font: Specifies a font size and name for use in the command-interpreter window.
Layout: Lets you specify the window and buffer size. Window size refers to the width in characters and height in lines of the command-interpreter window. Buffer size refers to the virtual size of the window when you use the horizontal and vertical scrollbars. It's a nice touch that the default buffer size is now 300 lines instead of the 25 lines it was in Windows NT.
Colors: Lets you specify colors for the screen text and background and for pop-up text and background.

When you change the properties of a command-prompt window and click OK, a dialog box appears asking you whether you want to apply the properties to the current command-interpreter window only (in which case the settings vanish when you close this window) or to future windows of the same title or started from the same shortcut (in which case the changes you made are persistent). If you want your settings to be persistent, you can avoid this annoyance by selecting Defaults instead of Properties when you right-click on the titlebar of the command-prompt window.

Running Multiple Commands

You can use conditional processing symbols to run multiple commands as a single command, with a command to the right of a conditional processing symbol processing the results of the command to the left of the symbol. Table 5-2 lists the conditional processing symbols that are available.

Table 5-2. Conditional processing symbols

Symbol	Syntax	Comment
& [...]	Command1 & Command2	Runs the first command, then the second.
&& [...]	Command1 && Command2	Runs the second command only if the first completed successfully.
[...]	Command1 Command2	Runs the second command only if the first command failed.
( ) [...]	(Command1 & Command2)	Group commands together.
; or ,	Command1 Parm1;Parm2	Separates command parameters.

Environment Variables

An environment variable is a string that contains information used to control some aspect of the operating system or application, such as the path to an important system file or directory, the number and type of processors on the motherboard, and so on. The two types of environment variables are:

System variables: These are the same for all users who log on to the computer, and their effect applies to the whole operating system. Only members of the Administrators group can create or modify system variables, and some default ones can't be modified at all.
Local variables: These differ for each user who logs on to the computer, and users can create and modify their own user variables and assign them values. Local variables were formerly called user variables in W2K and earlier.

Table 5-3 lists the system environment variables defined in WS2003 together with their default values, while Table 5-4 does the same for local environment variables.

Table 5-3. System environment variables and their default values

Variable	Description	Default value
%CMDEXTVERSION%	Version number of current command processor extensions	2
%COMPUTERNAME%	Name of computer
%COMSPEC%	Exact path to cmd.exe	C:\Windows\system32 \cmd.exe
%DATE%	Current date (see date )
%ERRORLEVEL%	Error code of most recently executed command (nonzero value indicates error)
%HOMEDRIVE%	Drive letter connected to user's home directory
%HOMEPATH%	Full path of user's home directory
%HOMESHARE%	Network path to user's shared home directory
%NUMBER_OF_ PROCESSORS%	Number of processors in computer
%OS%	Operating system name	Windows_NT
%PATH%	Search path for executable files	C:\Windows\system32; C:\Windows; C:\Windows\system32 \Wbem
%PATHEXT%	List of the file extensions considered executable	.COM;.EXE;.BAT;.CMD; .VBS;.VBE;.JS;.JSE;. WSF;.WSH;.VBS
%PROCESSOR_ ARCHITECTURE%	Chip architecture of the processor
%PROCESSOR_ IDENTFIER%	Description of the processor
%PROCESSOR_ LEVEL%	Model number of the processor installed on the computer
%PROCESSOR_ REVISION%	Revision number of the processor
%RANDOM%	Random decimal number between 0 and 32767
%SYSTEMDRIVE%	System root drive	C:
%SYSTEMROOT%	Location of OS root directory	C:\Windows
%TIME%	Current time (see `time` )
%WINDIR%	Location of OS directory	C:\Windows

Table 5-4. Local environment variables and their default values

Variable	Description	Default value
%ALLUSERSPROFILE%	Location of all users profile	C:\Documents and Settings \All Users
%APPDATA%	Default location where applications store data	C:\Documents and Settings \current_user \Application Data
%CD%	Current directory string
%CMDCMDLINE%	Exact command used to start current command shell
%LOGONSERVER%	Name of domain controller that validated current logon session
%PROMPT%	Command prompt settings for current command shell
%TEMP% and %TMP%	Default temporary directories used by applications for currently logged-on user	C:\Documents and Settings \current_user \Local Settings \Temp
%USERDOMAIN%	Name of domain containing currently logged-on user's account
%USERNAME%	Name of currently logged-on user
%USERPROFILE%	Location of profile for currently logged-on user

Working with Environment Variables

To set (create, delete, or modify) environment variables using the GUI:

Control Panel System Advanced Environment Variables {New Edit Delete}

To set a variable from the command line, use the set command (see set later in this chapter).

Only a member of the Administrators group can add, delete, or set the value of a system environment variable. Changes made by the currently logged-on user affect the user environment variables only for that user. You may have to reboot your system or close and reopen your application for the new value of an environment variable to take effect.

System variables may be used to define paths for logon scripts, home directories, and user profiles. They may also be used within logon scripts or in commands executed at the command prompt. To use an environment variable, enclose it in percent signs. For example, typing the command:

 C:\>  cd %windir%

produces the following result:

 C:\Windows>

You can easily display the value of an environment variable from the command line. For example, to display the name of the installed operating system using the OS system variable, just type:

 C:\>  echo %os%

which produces the result:

 Windows_NT

Who says WS2003 isn't really just Windows NT disguised?

Notes

Use double quotes to enclose commands that contain spaces.
Use && to separate multiple commands surrounded by quotes in a single command line.
Note that /x is the same as /e:on and /y is the same as /e:off for backward compatibility with the Windows NT command shell.
Installing new operating-system components or applications may create additional environment variables or modify existing ones such as PATH.