COMMAND.COM

COMMAND.COM
Other namesMS-DOS Prompt,
Windows Command Interpreter
DevelopersSeattle Computer Products, IBM, Microsoft, The Software Link, Datalight, Novell, Caldera
Release1980; 46 years ago (1980)
Written inx86 assembly language
Operating system
Platform16-bit x86
Successorcmd.exe
TypeCommand-line interpreter
COMMAND.COM running in a Windows console on Windows 95 (MS-DOS Prompt)

COMMAND.COM is the default command-line interpreter for MS-DOS, Windows 95, Windows 98 and Windows Me. In the case of DOS, it is the default user interface as well. It has an additional role as the usual first program run after boot (init process). As a shell, COMMAND.COM has two distinct modes of operation: interactive mode and batch mode. Internal commands are commands stored directly inside the COMMAND.COM binary; thus, they are always available, but can only be executed directly from the command interpreter.

Description

COMMAND.COM's successor on OS/2 and Windows NT systems is cmd.exe, although it is available in virtual DOS machines on IA-32 versions of those operating systems as well. The COMMAND.COM filename was also used by Disk Control Program [de] (DCP), an MS-DOS derivative by the former East German VEB Robotron.

COMMAND.COM is a DOS program. Programs launched from it are DOS programs that use the DOS API to communicate with the disk operating system. The compatible command processor under FreeDOS is sometimes also called FreeCom.

Operating modes

As a shell, COMMAND.COM has two distinct modes of operation. The first is interactive mode, in which the user types commands which are then executed immediately. The second is batch mode, which executes a predefined sequence of commands stored as a text file with the .BAT extension.

Internal commands

Internal commands are commands stored directly inside the COMMAND.COM binary. Thus, they are always available but can only be executed directly from the command interpreter.

All commands are executed after the ↵ Enter key is pressed at the end of the line. COMMAND.COM is not case-sensitive, meaning commands can be typed in any mixture of upper and lower case.

BREAK
Controls the handling of program interruption with Ctrl+C or Ctrl+Break.
CHCP
Displays or changes the current system code page.
CHDIR, CD
Changes the current working directory or displays the current directory.
CLS
Clears the screen.
COPY
Copies one file to another (if the destination file already exists, MS-DOS asks whether to replace it). (See also XCOPY, an external command that could also copy directory trees).
CTTY
Defines the device to use for input and output.
DATE
Display and set the date of the system.
DEL, ERASE
Deletes a file. When used on a directory, deletes all files inside the directory only. In comparison, the external command DELTREE deletes all subdirectories and files inside a directory as well as the directory itself.
DIR
Lists the files in the specified directory.
ECHO
Toggles whether the commands executed by a batch file are displayed on screen (ECHO ON) or not (ECHO OFF). Also displays text on the screen (ECHO text).
EXIT
Exits from COMMAND.COM and returns to the program which launched it.
LFNFOR
Enables or disables the return of long filenames by the FOR command. (Windows 9x).[citation needed]
LOADHIGH, LH
Loads a program into upper memory (HILOAD in DR DOS).
LOCK
Enables external programs to perform low-level disk access to a volume. (MS-DOS 7.1 and Windows 9x only)[citation needed]
MKDIR, MD
Creates a new directory.
PATH
Displays or changes the value of the PATH environment variable which controls the places where COMMAND.COM will search for executable files.
PROMPT
Displays or change the value of the PROMPT environment variable which controls the appearance of the prompt.
RENAME, REN
Renames a file or directory.
RMDIR, RD
Removes an empty directory.
SET
Sets the value of an environment variable; without arguments, shows all defined environment variables.
TIME
Display and set the time of the system.
TRUENAME
Display the fully expanded physical name of a file, resolving ASSIGN, JOIN and SUBST logical filesystem mappings.
TYPE
Display the content of a file on the console.
UNLOCK
Disables low-level disk access. (MS-DOS 7.1 and Windows 9x only)[citation needed]
VER
Displays the version of the operating system.
VERIFY
Enable or disable verification of writing for files.
VOL
Shows information about a volume.

Batch file commands

Control structures are mostly used inside batch files, although they can also be used interactively.

:label
Defines a target for GOTO.
CALL
Executes another batch file and returns to the old one and continues.
FOR
Iteration: repeats a command for each out of a specified set of files.
GOTO
Moves execution to a specified label. Labels are specified at the beginning of a line, with a colon (:likethis).
IF
Conditional statement, allows branching of the program execution.
PAUSE
Halts execution of the program and displays a message asking the user to press any key to continue.
REM
comment: any text following this command is ignored.
SHIFT
Replaces each of the replacement parameters with the subsequent one (e.g. %0 with %1, %1 with %2, etc.).

IF command

On exit, all external commands submit a return code (a value between 0 and 255) to the calling program. Most programs have a certain convention for their return codes (for instance, 0 for a successful execution).

If a program was invoked by COMMAND.COM, the internal IF command with its ERRORLEVEL conditional can be used to test on error conditions of the last invoked external program.[citation needed]

Under COMMAND.COM, internal commands do not establish a new value.[citation needed]

Variables

Batch files for COMMAND.COM can have four kinds of variables:

Redirection, piping, and chaining

Because DOS is a single-tasking operating system, piping is achieved by running commands sequentially, redirecting to and from temporary files.[citation needed] In DOS 2, pipe creates 2 temporary files: \%PIPE1.$$$ (input), and \%PIPE2.$$$ (output) (they get swapped after each command). COMMAND.COM makes no provision for redirecting the standard error channel.[citation needed]

command < filename
Redirect standard input from a file or device
command > filename
Redirect standard output, overwriting target file if it exists.
command >> filename
Redirect standard output, appending to target file if it exists.
command1 | command2
Pipe standard output from command1 to standard input of command2
command1command2
Commands separated by ASCII-20 (¶, invoked by Ctrl+T) are executed in sequence (chaining of commands). In other words, first command1 is executed until termination, then command2. This is an undocumented feature in COMMAND.COM of MS-DOS/PC DOS 5.0 and higher. It is also supported by COMMAND.COM of the Windows NT family as well as by DR-DOS 7.07. All versions of DR-DOS COMMAND.COM already supported a similar internal function utilizing an exclamation mark (!) instead (a feature originally derived from Concurrent DOS and Multiuser DOS) - in the single-user line this feature was only available internally (in built-in startup scripts like "!DATE!TIME") and indirectly through DOSKEY's $T parameter to avoid problems with ! as a valid filename character. 4DOS supports a configurable command line separator (4DOS.INI CommandSep= or SETDOS /C), which defaults to ^. COMMAND.COM in newer versions of Windows NT also supports an & separator for compatibility with the cmd syntax in OS/2 and the Windows NT family. (cmd does not support the ¶ separator.)

Limitations

Generally, the command line length in interactive mode is limited to 126 characters. In MS-DOS 6.22, the command line length in interactive mode is limited to 127 characters.[citation needed]

See also