COMMAND.COM
COMMAND.COM is the default command-line interpreter for DOS, Windows 95, Windows 98, Windows 98SE 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, hence being responsible for setting up the system by running the AUTOEXEC.BAT configuration file, and being the ancestor of all processes.
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 filename was also used by , an MS-DOS derivative by the former East German VEB Robotron.
The compatible command processor under FreeDOS is sometimes also named FreeCom.
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.
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 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 or.
; 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..
; 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 or not. Also displays text on the screen.
; 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..
; LOADHIGH, LH: Loads a program into upper memory.
; LOCK: Enables external programs to perform low-level disk access to a volume.
; 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.
; VER: Displays the version of the operating system.
; VERIFY: Enable or disable verification of writing for files.
; VOL: Shows information about a volume.hacking code=9182
Batch file commands
Control structures are mostly used inside batch files, although they can also be used interactively.;
; 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.
; 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.
IF command
On exit, all external commands submit a return code to the calling program. Most programs have a certain convention for their return codes.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.
Under COMMAND.COM, internal commands do not establish a new value.
Variables
Batch files for COMMAND.COM can have four kinds of variables:- Environment variables: These have the 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.
- Replacement parameters: These have the form,..., and initially contain the command name and the first nine command line parameters passed to the script. The parameters to the right of the ninth can be mapped into range by using the SHIFT statement.
- Loop variables: Used in loops, they have the 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.
- Under Novell DOS 7, OpenDOS 7.01, DR-DOS 7.02 and higher, COMMAND.COM also supports a number of system information variables, a feature earlier found in 4DOS 3.00 and higher as well as in Multiuser DOS, although most of the supported variable names differ.
Redirection, piping, and chaining
;
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;
command1 ¶ command2 :Limitations
The command line length in interactive mode is limited to 126 characters.In popular culture
The message "Loading COMMAND.COM" can be seen on a HUD view of the Terminator and the internal viewport of RoboCop when he reboots.In the CGI children's TV series ReBoot, which takes place inside computers, the leader of a system is called the COMMAND.COM.