Command-line interpreter

RT-11 running on UKNC

Sample screenshot of the command-line interpreter Bash.

A command-line interpreter (also command line shell, command language interpreter) is a computer program that reads lines of text entered by a user and interprets them in the context of a given operating system or programming language.

Command-line interpreters as user interfaces

Command-line interpreters allow users to issue various commands in a very efficient (and often terse) way. This requires the user to know the names of the commands and their parameters, and the syntax of the language that is interpreted. From the 1960s onwards, user interaction with computers was primarily by means of command-line interfaces.

In the 1970s, researchers began to develop graphical user interfaces (GUIs) to provide an alternative user interface for computers, whereby commands were represented by pictorial operations, rather than as textual descriptions and these have become the most common way of interacting with a computer. However, command-line interpreters remain widely used in conjunction with GUIs. For some complex tasks, the latter are less effective because of the large number of menus and dialog boxes presented and because of the innate difficulty of representing the underlying task graphically.

Scripting

Most command-line interpreters support scripting, to various extents. (They are, after all, interpreters of an interpreted programming language, albeit that in many cases the language is unique to the particular command-line interpreter.) They will interpret scripts (variously termed shell scripts or batch files) written in the language that they interpret. Some command-line interpreters also incorporate the interpreter engines of other languages, such as REXX, in addition to their own, allowing the executing of scripts, in those languages, directly within the command-line interpreter itself.

Conversely, scripting programming languages, in particular those with an eval function (such as REXX, Perl, Python, Ruby or Jython), can be used to implement command-line interpreters. For a few operating systems, most notably DOS, such a command interpreter provides a more flexible command line interface than the one supplied. In other cases, such a command interpreter can present a highly customised user interface employing the user interface and input/output facilities of the language.

Quotes

Although most users think of the shell as an interactive command interpreter, it is really a programming language in which each statement runs a command. Because it must satisfy both the interactive and programming aspects of command execution, it is a strange language, shaped as much by history as by design.

– Brian Kernighan & Rob Pike ^[1]

Examples

• 4DOS - (DOS, Windows)
• 4NT - (Windows NT)
• 4OS/2 - (OS/2)
• Amiga CLI/Amiga Shell - (AmigaOS)
• Apple DOS/Apple ProDOS, had built-in BASIC interpreter, used on the Apple II, preceding the Macintosh
• CL - (OS/400)
• Basic-Plus - (RSTS/E)
• cmd.exe - (OS/2, Windows CE 3.0, Windows NT - Windows 7)
• CMS - (VM/CMS)
• COMMAND.COM - (DOS, Windows 95 - Windows Vista)
• Commodore DOS Wedge - (Commodore 64)
• DCL - (OpenVMS)
• EFI-SHELL - (Extensible Firmware Interface)
• GMLCMD - (Windows)
• iSeries QSHELL - (IBM OS/400)
• SymShell - (SymbOS)
• TSO - (MVS, z/OS)
• Unix shell programs such as sh, Bash, ksh, csh and others
• Tclsh and Wish, shells used with the Tcl language in its various implementations
• The above Unix shells implemented under other OSes including Windows NT/2000/Xp/2003 OS series and with diminished capabilities under the MS-Dos/Windows 95/98/Me series: MKS Toolkit (Bourne, Bash, Korn, C shells, rsh, tclsh and SSH), Microsoft Windows Services for Unix (C and Korn shells), AT&T U/Win (all or most shells), Cygwin, etc.
• Newer Unix shells under various OSes and environments such as the enhanced Korn variant zsh, the Perl-based psh shell etc.
• Windows PowerShell - (Windows XP - Windows 7)
• Windows Recovery Console - (Windows 2000, Windows XP and Windows Server 2003)
• YouShell - (YouOS)

See also

• Shell (computing)
• Comparison of computer shells
• Text terminal
• Command line argument
• Read-eval-print loop
• Batch processing
• Batch file
• Shell script
• Scripting language
• Domain-specific programming language
• clig for tcl/c

References

External links

• Command Line Warriors website — focus on GNU/Linux
• The Command Line in Windows website — DOS and Windows