Jump to content

COMMAND.COM

From Wikipedia, the free encyclopedia
"COMMAND" redirects here. For other uses, see Command.
Not to be confused with cmd.exe.

COMMAND.COM
Other namesMS-DOS Prompt,
Windows Command Interpreter
Developer(s)Seattle Computer Products, IBM, Microsoft, The Software Link, Datalight, Novell, Caldera
Initial release1980; 44 years ago (1980)
Written inx86 assembly language[1]
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

[edit]

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.[2] It has an additional role as the usual first program run after boot (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 OS/2 and Windows NT systems is cmd.exe, although COMMAND.COM 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.[3]

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

Operating modes

[edit]

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

[edit]

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 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.[4]
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

[edit]

Control structures are mostly used inside batch files, although they can also be used interactively.[5][4]

: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

[edit]

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).[6][7][8][9]

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

[edit]

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

  • Environment variables: These have the %VARIABLE% form and are associated with values with the SET statement. Before DOS 3 COMMAND.COM will only expand environment variables in batch mode; that is, not interactively at the command prompt.[citation needed]
  • Replacement parameters: These have the form %0, %1...%9, and initially contain the command name and the first nine command-line parameters passed to the script (e.g., if the invoking command was myscript.bat John Doe, then %0 is "myscript.bat", %1 is "John" and %2 is "Doe"). The parameters to the right of the ninth can be mapped into range by using the SHIFT statement.[citation needed]
  • Loop variables: Used in loops, they have the %%a format when run in batch files. These variables are defined solely within a specific FOR statement, and iterate over a certain set of values defined in that FOR statement.[citation needed]
  • Under Novell DOS 7, OpenDOS 7.01, DR-DOS 7.02 and higher, COMMAND.COM also supports a number of system information variables,[5][10][4] a feature earlier found in 4DOS 3.00 and higher[11] as well as in Multiuser DOS,[4] although most of the supported variable names differ.

Redirection, piping, and chaining

[edit]

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).[4] In other words, first command1 is executed until termination, then command2.[4] This is an undocumented feature in COMMAND.COM of MS-DOS/PC DOS 5.0 and higher.[4] 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.[4] 4DOS supports a configurable command line separator (4DOS.INI CommandSep= or SETDOS /C), which defaults to ^.[11] 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.[11] (cmd does not support the ¶ separator.)

Limitations

[edit]

Generally, the command line length in interactive mode is limited to 126 characters.[12][13][14] In MS-DOS 6.22, the command line length in interactive mode is limited to 127 characters.[citation needed]

[edit]
  • The message "Loading COMMAND.COM" can be seen on a HUD view of the Terminator and the internal viewport of RoboCop when he reboots.[citation needed]
  • In the animated children's TV series ReBoot, which takes place inside computers, the leader of a system (the equivalent of a city) is called the COMMAND.COM.[citation needed]

See also

[edit]
  • 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
  • — third-party replacement command processors
  • DOSSHELL / ViewMAX — alternative DOS shells
  • — 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

[edit]
  1. ^ "MS-DOS/COMMAND.ASM at master · microsoft/MS-DOS". GitHub.
  2. ^ "MS-DOS | Definition, Features, Importance, & Facts | Britannica". www.britannica.com. Retrieved 2024-06-26.
  3. ^ 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.
  4. ^ 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]
  5. ^ a b "Chapter 7: Batch Processing". Caldera DR-DOS 7.02 User Guide. Caldera, Inc. 1998 [1993, 1997]. Archived from the original on 2017-09-11. Retrieved 2017-09-11.
  6. ^ 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]
  7. ^ Auer, Eric; Paul, Matthias R.; Hall, Jim (2015-12-24) [2003-12-31]. "MS-DOS errorlevels". Archived from the original on 2015-12-24.
  8. ^ 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]
  9. ^ Allen, William; Allen, Linda. "Windows 95/98/ME ERRORLEVELs". Archived from the original on 2005-10-29.
  10. ^ Caldera DR-DOS 7.02 User Guide. Caldera, Inc. 1998 [1993, 1997]. Archived from the original on 2016-11-04. Retrieved 2013-08-10.
  11. ^ a b c

    [...] Multiple Commands: You can type several commands on the same command line, separated by a caret [^]. For example, if you know you want to copy all of your .TXT files to drive A: and then run CHKDSK to be sure that drive A's file structure is in good shape, you could enter the following command: C:\>COPY *.TXT A: ^ CHKDSK A: You may put as many commands on the command line as you wish, as long as the total length of the command line does not exceed 511 characters. You can use multiple commands in aliases and batch files as well as at the command line. If you don't like using the default command separator, you can pick another character using the SETDOS /C command or the CommandSep directive in 4DOS.INI. [...] SETDOS /C: (Compound character) This option sets the character used for separating multiple commands on the same line. The default is the caret [^]. You cannot use any of the redirection characters [<>|], or the blank, tab, comma, or equal sign as the command separator. The command separator is saved by SETLOCAL and restored by ENDLOCAL. This example changes the separator to a tilde [~]: C:\>SETDOS /C~ (You can specify either the character itself, or its ASCII code as a decimal number, or a hexadecimal number preceded by 0x.) [...] CommandSep = c (^): This is the character used to separate multiple commands on the same line. [...] Special Character Compatibility: If you use two or more of our products, or if you want to share aliases and batch files with users of different products, you need to be aware of the differences in three important characters: the Command Separator [...], the Escape Character [...], and the Parameter Character [...]. The default values of each of these characters in each product is shown in the following chart: [...] Product, Separator, Escape Parameter [...] 4DOS: ^, ↑, & [...] 4OS2, 4NT, Take Command: &, ^, $ [...] (The up-arrow [↑] represents the ASCII Ctrl-X character, numeric value 24.) [...]

    — Brothers, Hardin; Rawson, Tom; Conn, Rex C.; Paul, Matthias R.; Dye, Charles E.; Georgiev, Luchezar I. (2002-02-27). 4DOS 8.00 online help.
  12. ^ 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]
  13. ^ 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]
  14. ^ Schulman, Andrew; Brown, Ralf D.; Maxey, David; Michels, Raymond J.; Kyle, Jim (1994) [November 1993]. Undocumented DOS: A programmer's guide to reserved MS-DOS functions and data structures - expanded to include MS-DOS 6, Novell DOS and Windows 3.1 (2 ed.). Reading, Massachusetts, US: Addison Wesley. pp. 623, 626. ISBN 0-201-63287-X. (xviii+856+vi pages, 3.5"-floppy) Errata: [6] [7]

Further reading

[edit]

[...] 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.
[edit]
  • COMMAND1.ASM on GitHub - Source code to COMMAND.COM version A067 released by Microsoft as part of MS-DOS 4.0
  • 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=1258399873"