COMMAND.COM

Source: Wikipedia, the free encyclopedia.
Not to be confused with cmd.exe.

COMMAND.COM
Windows console on Windows 95
(MS-DOS Prompt)

COMMAND.COM is the default

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 is the default

init process), hence being responsible for setting up the system by running the AUTOEXEC.BAT configuration file, and being the ancestor of all processes.[citation needed
]

COMMAND.COM's successor on

Disk Control Program [de] (DCP), an MS-DOS derivative by the former East German VEB Robotron.[2]

COMMAND.COM is a DOS program. Programs launched from COMMAND.COM are DOS programs that use the

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 text is displayed (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
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
JOIN and SUBST logical filesystem mappings.[3]
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.[4][3]

: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).[5][6][7][8]

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 a temporary file.[citation needed] 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).
4DOS.INI CommandSep= or SETDOS /C), which defaults to ^.[10] 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.[10]
 (cmd does not support the ¶ separator.)

Limitations

Generally, the command line length in interactive mode is limited to 126 characters.

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

In popular culture

See also

  • List of DOS commands
  • Comparison of command shells
  • cmd.exe — command-line interpreter in various Windows and OS/2 systems
  • — starts the command processor as the first process
  • SHELL (CONFIG.SYS directive)
    — to override default command processor
  • COMSPEC (environment variable)
    — set by COMMAND.COM to reload transient portion of itself
  • CMDLINE (environment variable)
    — set by COMMAND.COM to pass long command lines to external programs
    • NDOS
    — third-party replacement command processors
  • DOSSHELL / ViewMAX
    — alternative DOS shells
    • REAL/32
    — have similar command processors not named COMMAND.COM
  • PC-MOS/386 — has a similar command processor also named COMMAND.COM
  • Transient Program Area
    — memory available for use either by the running application or the transient portion of COMMAND.COM
  • SpartaDOS X — a similar implementation for Atari computers

References

  1. ^ "MS-DOS/COMMAND.ASM at master · microsoft/MS-DOS". GitHub.
  2. ^ Kurth, Rüdiger; Groß, Martin; Hunger, Henry (2016-11-29) [2007]. "Betriebssystem DCP". www.robotrontechnik.de (in German). Archived from the original on 2019-04-03. Retrieved 2019-04-28.
  3. ^ a b c d e f g h Paul, Matthias R. (1997-07-30) [1994-05-01]. NWDOS-TIPs — Tips & Tricks rund um Novell DOS 7, mit Blick auf undokumentierte Details, Bugs und Workarounds. Release 157 (in German) (3 ed.). Archived from the original on 2016-11-04. Retrieved 2014-08-06. {{cite book}}: |work= ignored (help) (NB. The provided link points to a HTML-converted version of the NWDOSTIP.TXT, which is part of the MPDOSTIP.ZIP collection.) [1]
  4. ^
    Caldera, Inc. 1998 [1993, 1997]. Archived from the original
    on 2017-09-11. Retrieved 2017-09-11.
  5. ^ Paul, Matthias R. (1997-05-01) [1993-10-01]. BATTIPs — Tips & Tricks zur Programmierung von Batchjobs (in German). Kapitel 7: ERRORLEVEL abfragen. Archived from the original on 2017-08-23. Retrieved 2017-08-23. {{cite book}}: |work= ignored (help) (NB. BATTIPS.TXT is part of MPDOSTIP.ZIP. The provided link points to an HTML-converted older version of the BATTIPS.TXT file.) [2]
  6. ^ Auer, Eric; Paul, Matthias R.; Hall, Jim (2015-12-24) [2003-12-31]. "MS-DOS errorlevels". Archived from the original on 2015-12-24.
  7. ^ Paul, Matthias R. (2003) [1997]. Auer, Eric (ed.). "Exitcodes (errorlevels) of DOS utilities". Archived from the original on 2017-09-11. Retrieved 2017-09-11. [3]
  8. ^ Allen, William; Allen, Linda. "Windows 95/98/ME ERRORLEVELs". Archived from the original on 2005-10-29.
  9. Caldera, Inc. 1998 [1993, 1997]. Archived from the original
    on 2016-11-04. Retrieved 2013-08-10.
  10. ^
    4DOS 8.00 online help
    .
  • ^ Paul, Matthias R. (1997-07-01) [1994-01-01]. MSDOSTIPs — Tips für den Umgang mit MS-DOS 5.0-7 (in German). Archived from the original on 2017-08-22. Retrieved 2013-10-25. {{cite book}}: |work= ignored (help) (NB. MSDOSTIP.TXT is part of MPDOSTIP.ZIP, maintained up to 2001 and distributed on many sites at the time. The provided link points to a HTML-converted older version of the MSDOSTIP.TXT file.) [4]
  • ^ Paul, Matthias R. (1997-05-01) [1995-03-01]. "Hinweise zu JPSofts 4DOS 5.5b/c, 5.51, 5.52a und NDOS". MPDOSTIP (in German). Archived from the original on 2016-11-04. Retrieved 2015-05-08. (NB. The provided link points to a HTML-converted version of the 4DOS5TIP.TXT file, which is part of the MPDOSTIP.ZIP collection.) [5]
  • ISBN 0-201-63287-X. (xviii+856+vi pages, 3.5"-floppy) Errata: [6] [7]

    • Further reading

    [...] all MS-DOS versions prior to Windows 95 [...] used a COM style COMMAND.COM file which has a special signature at the start of the file [...] queried by the MS-DOS BIOS before it loads the shell, but not by the DR-DOS BIOS [...] COMMAND.COM would [...] check that it is running on the "correct" DOS version, so if you would load their COMMAND.COM under DR-DOS, you would receive a "Bad version" error message and their COMMAND.COM would exit, so DR-DOS would [...] display an error message "Bad or missing command interpreter" (if DR-DOS was trying to load the SHELL= command processor after having finished CONFIG.SYS processing). In this case, you could enter the path to a valid DR-DOS COMMAND.COM (C:\DRDOS\COMMAND.COM) and everything was fine. Now, things have changed since MS-DOS 7.0 [...] COMMAND.COM has internally become an EXE style file, so there is no magic [...] signature [...] to check [...] thus no way for DR-DOS to rule out an incompatible COMMAND.COM. Further, their COMMAND.COM no longer does any version checks, but [...] does not work under DR-DOS [...] just crashes [...] the PC DOS COMMAND.COM works fine under DR-DOS [...]

    Paul, Matthias R. (2004-06-17). "Re: Random Lockups with DR-DOS 7.03". FidoNet conference: ALT_DOS. Archived from the original on 2019-04-28. Retrieved 2019-04-28.

    External links

    • COMMAND.ASM on GitHub – Source code to COMMAND.COM version 2.11 released by Microsoft as part of MS-DOS 2.0
    • COMMAND.ASM on GitHub – Source code to COMMAND.COM version 1.17 released by Microsoft as part of MS-DOS 1.25
    • FreeCom – COMMAND.COM implementation of FreeDOS
    Retrieved from "https://en.wikipedia.org/w/index.php?title=COMMAND.COM&oldid=1214536573"