Introduction to the Command Prompt

DOS is dead, long live the command line

Before proceeding further, I wish to clear up a common misconception that the command prompt in Windows XP is the same as DOS. Even some experts who know better sometimes refer to the command prompt as a “DOS window”. In fact, Microsoft itself isn't always careful about the distinction. There are some superficial resemblances and some commands with the same name but in fact the old 16-bit DOS is dead. All remnants of DOS are totally gone from the Windows XP kernel (there is a DOS emulator for legacy programs). Windows XP is a 32-bit protected memory system with a totally different approach from the DOS/9X/Me family. The command line in XP has many more capabilities and none of the 16-bit limitations like the restriction to the DOS 8.3 file name format. The augmented capabilities make the command line a powerful tool.

The command prompt window

The command prompt is run from its own window by invoking the Windows XP command interpreter that is provided by the file cmd.exe located in the folder \Windows\System32\. (The old DOS command interpreter is command.com.) If you look in this folder you may also see several files that look suspiciously like some of the old DOS files. They are, however, different 32-bit versions with many new features. The command prompt window can be opened by entering "cmd" (without quotes) into Start-Run or through Start-All Programs-Accessories. A black and white window (the colors can be changed) containing the command prompt will open. The window looks just like the old DOS window but don’t be fooled, it isn’t. Note that it is possible to open several windows containing command prompts, all running independently. It is even possible to run a separate command prompt shell inside another command prompt window.

Internal and external commands

There are two kinds of commands that can be run from the command prompt. There are the internal commands that are built into the command interpreter like “del” and “dir”. These commands can only be run from a command prompt (or by invoking the command interpreter in some other way). They are listed in the table below. There is also a large list of external commands that use an additional executable file that can be run from either the command prompt or the Start-Run line. Details of the various commands are available in several places. In the Professional version of Windows XP there is a help file ntcmds.chm, which has details of all the commands and their many switches. The help file can be opened by entering (without the quotes) "hh ntcmds.chm" into Start-Run. It may or may not be in the Home Edition, depending on what setup you have. However, in both versions a list of many (but not all) of the commands available can be obtained by entering "help" (without quotes) into a command prompt. For more detail on a specific command, enter "help command-name" or "command-name /?" For example to get information on the command xcopy, enter "help xcopy" or "xcopy /?”. Microsoft keeps moving things, but the last time I checked they had a command line reference at this link. Some of the commonly used commands are discussed on this page and in the list given here.

Table I. Internal commands in the command shell

assoc	dir	move	set
break	echo	path	setlocal
call	endlocal	pause	shift
cd	exit	popd	start
cls	for	prompt	time
color	ftype	pushd	title
copy	goto	rd	type
date	if	rem	verify
del	md	ren	volume

Some symbols that are used

In addition to the commands, there are several symbols that are used. These modify or combine the actions of commands. The table below gives a list.

Table II. Symbols used with commands

Symbol	Function	Example
>	Sends output to a named file. If file does not exist, it creates one. Overwrites existing file	command > somefile
>>	Appends output to contents of a named file or creates a file if none exists	command >> somefile
<	Uses contents of a named file as input to a command	command <>
¦	Sends ("pipes") the output of command1 to the input of command2	command1 ¦ command2
&	Used to combine two commands. Executes command1 and then command2	command1 & command2
&&	A conditional combination. Executes command2 if command1 completes successfully	command1 && command2
¦¦	Command2 executes only if command1 does not complete successfully.	command1 ¦¦ command2
@	Used in batch files at the beginning of a line to turn off the display of commands	@echo off

The most commonly used symbols are the two redirection symbols ">" and ">>" and the so-called pipe, "¦" . (Just to make sure there is no confusion, the "pipe" is the symbol above the back slash on most keyboards. On keyboards it has a break in the middle but the break does not always show when you type the symbol. A special code is used to show it on a Web page.)