- Aug 27, 2001
Understanding the Elements of a DOS Command
To begin to understand DOS commands, you first need to know a few fundamental facts:
DOS requires that you use a specific set of rules, or syntax, when you issue commands.
All DOS commands begin with a keyword that identifies the action you want performed.
Parameters, which are a part of a command's syntax, refine the way a command is executed.
Syntax is the order in which you type the elements of the DOS commandits grammar. If you say, "Ball red the choose I," people probably will not understand that you are trying to say, "I choose the red ball." Some people might understand what you are trying to say, but not many. A computer, on the other hand, has no intelligence or imagination; it can interpret commands only according to its programming. Programming several optional syntaxes for commands requires using a great deal of extra memory and disk space, which cuts down on the resources available to do real work. That's why you have to supply the intelligence and imagination and why you must enter DOS commands precisely according to the rules of command syntax.
You can think of the command keyword as the action part, or verb, of a DOS command. In addition to the keyword, many commands require or allow further directions. You supply these directions as parameters and switches. Parameters tell DOS what action to take or how to apply the action. Using DOS commands is easy as long as you follow the rules of order and use the correct parameters. After you know the basic rules, you often can figure out parameters for commands that you don't use on a regular basis.
You run applications softwaresuch as word processors or drawing programsby entering a command at the DOS prompt. The command you use to start an application is the name of the program file (COM or EXE) in which the programming for the software is stored.
Most applications software incorporates the issuing of commands as part of the software's operation. The commands discussed in this book are DOS commands. Be sure that you know the difference between DOS commands, which you issue at the DOS command line, and the commands you learn to use with your applications software.
If you are unsure whether a command you have been taught to use is part of DOS, look in Appendix F, "Command Reference." If that command is not listed, it is an application program command, not a DOS command.
The Command Syntax
The syntax for most DOS commands can be boiled down to one of the following two simple formats:
KEYWORD Drive\Files Switches KEYWORD SourceFiles TargetFiles Switches
A DOS command always begins with the keyword, which is the name of the command, followed by a space. If you use the language metaphor, the keyword is the verb that specifies the action to be taken.
The first example shows the common form for DOS commands that don't change files in some way. The Drive\Files portion of the example is a parameter that specifies what drive or files on which the command is supposed to act. This parameter is analogous to a noun in English. In other words, the parameter is the thing on which the verb acts. This portion of the syntax is in italic to show that the parameter is optional. The parameter also can be followed by command-line switches. To extend the language metaphor, switches are like adverbs; they modify the verb. They change the action to be done.
The second example here is typical of the syntax for most DOS commands that operate on groups of files. The keyword, of course, specifies the action, followed by two parameters that indicate the disk or files that provide the data source for the action. The second parameter indicates the target disk or files. To copy a group of files from one disk or directory to another, for example, you can use the following command:
COPY A:Myfile.TXT B:Yourfile.TXT
This command copies a file having the name MYFILE.TXT on drive A into the memory of your computer and then writes the contents of the file onto drive B using the name YOURFILE.TXT.
Some parameters or switches are optional, meaning that some parts of the command syntax, such as the keyword, are mandatory. When you enter only the mandatory command elements, DOS (in most cases) uses default parameters for other elements.
A good example is the COPY command. If the following is the command, the default target is the currently logged disk and directory:
If you're in C:\TEMP, the file is copied to that directory, and the current filename, MYFILE.TXT, is the target filename as well.
As you can see, having defaults makes commands easier to use and shorter, and gives you fewer opportunities to make mistakes.
Because many DOS commands have several parameters, switches, and defaults, different forms of these commands might be correct. You seldom, if ever, use all the optional syntax for any command. Some switches actually are mutually exclusive. You cannot format a floppy disk as both high density and low density, for example.
To find out what options are available for any given command, you should look up the command in the "Command Reference" later in this book. The first time you look up a complex command, don't let the sheer volume of optional parameters and switches throw you for a loop. Even the simplest of DOS commands has several options.
The way the syntax is presented often is called the paradigm. Even the simple DOS commands have an imposing paradigm. A good example is the DIR command, a real workhorse of a command. Its paradigm looks something like the following:
DIR filespec /P /W /S /B /L /C /CH /O:sortorder /A:attributes
You use the DIR command to display a directory of one or more files stored on a disk. This command might look formidable, but it is much easier to understand if you break down the individual components.
→ For a description of the DIR command and its options, see "Listing Files with the DIR Command" in Chapter 8, "Managing Your Files", p. 193.
The Command-Line Parameters
In addition to the command's name, a DOS command contains syntax elements known as parameters. Parameters (sometimes called arguments) are the parts of a command line that provide DOS with the objects of the command's action. The objects might be files, system settings, or hardware devices.
In the DIR example in the preceding section, filespec is the complete filename, including any drive, path, and wildcards that you want the DIR command to use. In some commands, you might see the filespec spelled out, as in the following:
Don't be confused by this formal rendering of the filespec; it simply states that the filespec can contain a drive letter, a pathname, a filename, and an extension.
Many new users are confused about the way slashes and backslashes are used in commands. In actuality, their uses are stated simply in two rules:
Backslashes (\) are used as separators (delimiters) when specifying directory and file information.
Slashes (/), sometimes called forward slashes, are used as signals to DOS that the next character is a command-line switch.
A good memory association to use is that a backslash connects one name back to the name that comes before it, whereas a slash connects to the character in front of it.
The Optional Switches
A switch is a parameter that turns on an optional function of a command. Switches are special parameters because they usually are not the objects of a command's action; rather, switches modify the command's action. You can use the /W switch with the DIR command, for example, to display a wide directory of files instead of the usual single-column list. Switches can make a basic command more versatile and powerful. In the DIR example, /P, /W, /S, /B, /L, /O, /C, /CH, and /A are switches.
Usually, you can use a command's switches in any order or any combination. Not all DOS commands have switches, however. Also, the letter used for a switch in one DOS command might have a different meaning in another DOS command. In addition, some switches require a parameter. You usually attach switch parameters to the switch by using a colon (:), as in the following example:
FORMAT A: /F:360 /S
In this example, the /F switch specifies that a 360KB floppy disk be formatted in a disk drive that normally uses high-density (1.2MB) disks.