Managing Command Shell

Managing Command Shell Startup

When you previously worked with the command line, you probably started it by clicking Start, pointing to Programs or All Programs, Accessories, and then choosing Command Prompt. Another way to start a command line is to use the Run dialog box or type cmd in an open command-shell window. These techniques enable you to pass arguments to the command line, including switches that control how the command line works as well as parameters that execute additional commands. For example, you can start the command shell in quiet mode (meaning command echo is turned off) by using the startup command cmd /q and if you wanted the command shell to execute a command and then terminate, you could type cmd /c followed by the command text enclosed in quotation marks. The following example starts a command shell, sends the output of ipconfig to a file, and then exits the command shell:

cmd /c "ipconfig > c:\ipconfig.txt"

Table 2-1 summarizes the key parameters for the Windows command shell (Cmd.exe). Note that several command-line parameters are set by default. Because of this, the command line normally uses standard ANSI character codes for command output, as opposed to Unicode character codes, and enables command extensions that add features to most built-in commands.

Table 2-1: Essential Parameters for the Command Line

Parameter	Description
/C	Executes the command specified and then exits the command shell.
/K	Executes the command specified and then remains in interactive mode.
/A	Command output to files (or pipes) is set to ANSI format (default).
/U	Command output to files (or pipes) is set to Unicode.
/U	Turns on quiet mode, meaning command echo is off. By default, command echo is on.
/T:FG	Sets the foreground and background colors for the console window.
/E:ON	Enables command extensions, which is the default.
/E:OFF	Disables command extensions.

Note

Some parameters cannot be used with other switches. For example, you can’t enable both Unicode and ANSI character codes. If you use both /A and /U, or /E:ON and /E:OFF, the command line applies the last option you passed on the command line.

Sometimes you may want to use different environment settings or parameters for a command line and then go back to your original settings without exiting the console window. To do this, you can use a technique called nesting. With nesting, you start a command line within a command line and the nested command line inherits its environment settings from the current command line. You can then modify the environment as necessary and execute commands and scripts using those settings. When you type exit to end the nested command- line instance, you return to the previous command line and the previous environment settings are restored.

Tip

As you set out to work with the command shell, keep in mind that some characters have special meanings and that whenever the command shell encounters one of these characters, it attempts to carry out the special procedure associated with that character. Special characters include < > ( ) & | @ ^. If you want to use a special character as a regular character, you must escape the special character for the command shell to look at it literally, without invoking the special procedures with which it is associated. The escape character is the caret (^), which is the character above the 6 key on a standard keyboard, and is placed to immediately precede the special character.