|Original author(s)||Ken Thompson|
|Developer(s)||AT&T Bell Laboratories|
|Initial release||November 3, 1971|
|Operating system||Unix and Unix-like|
The Thompson shell is the first Unix shell, introduced in the first version of Unix in 1971, and was written by Ken Thompson.It was a simple command interpreter, not designed for scripting, but nonetheless introduced several innovative features to the command-line interface and led to the development of the later Unix shells.
A Unix shell is a command-line interpreter or shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting language, and is used by the operating system to control the execution of the system using shell scripts.
A command-line interface or command language interpreter (CLI), also known as command-line user interface, console user interface and character user interface (CUI), is a means of interacting with a computer program where the user issues commands to the program in the form of successive lines of text. A program which handles the interface is called a command language interpreter or shell.
The name "shell" for a command-line interpreter and the concept of making the shell a user program outside of the operating system kernel were introduced in Unix's precursor Multics.
Multics is an influential early time-sharing operating system which is based on the concept of a single-level memory. Virtually all modern operating systems were heavily influenced by Multics – often through Unix, which was created by some of the people who had worked on Multics – either directly or indirectly.
An early feature of the Thompson shell was a compact syntax for input/output redirection. In Multics, redirecting the input or output of a command required separate commands to start and stop redirection; in Unix, one could simply add an argument to the command line consisting of the < symbol followed by a filename for input or the > symbol for output, and the shell would redirect I/O for the duration of the command. This syntax was already present by the release of the first version of Unix in 1971.
A later addition was the concept of pipes. At the suggestion of Douglas McIlroy, the redirection syntax was expanded so that the output of one command could be passed to the input of another command. The original pipe syntax, as described in the Version 3 manual, was:
In Unix-like computer operating systems, a pipeline is a mechanism for inter-process communication using message passing. A pipeline is a set of processes chained together by their standard streams, so that the output text of each process (stdout) is passed directly as input (stdin) to the next one. The first process is not completed before the second is started, but they are executed concurrently. The concept of pipelines was championed by Douglas McIlroy at Unix's ancestral home of Bell Labs, during the development of Unix, shaping its toolbox philosophy. It is named by analogy to a physical pipeline. A key feature of these pipelines is their "hiding of internals". This in turn allows for more clarity and simplicity in the system.
Malcolm Douglas McIlroy is a mathematician, engineer, and programmer. As of 2007 he is an Adjunct Professor of Computer Science at Dartmouth College. McIlroy is best known for having originally developed Unix pipelines, software componentry and several Unix tools, such as spell, diff, sort, join, graph, speak, and tr.
This syntax proved too ambiguous and was easily confused with redirection to and from files—the system cannot tell if "command2" is the command "command2" or the file "command2". By Version 4, the syntax had changed to use both the | and ^ symbols to denote pipes:
command1 | command2
This produces exactly the same result as:
command1 ^ command2
The > symbol changed into:
command1 > file1
This would put the output of command1 into file1.
The Thompson shell syntax for redirection with < and >, and piping with |, has proven durable and has been adopted by most other Unix shells and command shells of several other operating systems, most notably on DOS, OS/2 and Microsoft Windows.
DOS is a platform-independent acronym for disk operating system which became common shorthand for the popular family of disk operating systems for x86-based IBM PC compatibles. DOS primarily consists of Microsoft's MS-DOS and a rebranded IBM version under the name PC DOS, both of which were introduced in 1981. Later compatible systems from other manufacturers are DR DOS, ROM-DOS, PTS-DOS, Embedded DOS, FreeDOS (1998), and RxDOS. MS-DOS dominated the IBM PC compatible market between 1981 and 1995.
OS/2 is a series of computer operating systems, initially created by Microsoft and IBM under the leadership of IBM software designer Ed Iacobucci. As a result of a feud between the two companies over how to position OS/2 relative to Microsoft's new Windows 3.1 operating environment, the two companies severed the relationship in 1992 and OS/2 development fell to IBM exclusively. The name stands for "Operating System/2", because it was introduced as part of the same generation change release as IBM's "Personal System/2 (PS/2)" line of second-generation personal computers. The first version of OS/2 was released in December 1987 and newer versions were released until December 2001.
Microsoft Windows is a group of several graphical operating system families, all of which are developed, marketed and sold by Microsoft. Each family caters to a certain sector of the computing industry. Active Microsoft Windows families include Windows NT and Windows IoT; these may encompass subfamilies, e.g. Windows Server or Windows Embedded Compact. Defunct Microsoft Windows families include Windows 9x, Windows Mobile and Windows Phone.
The shell's design was intentionally minimalistic; even the if and goto statements, essential for control of program flow, were implemented as separate commands.As a result, by the 1975 release of Version 6 Unix, it was becoming clear that the Thompson shell was inadequate for most serious programming tasks.
Sixth Edition Unix, also called Version 6 Unix or just V6, was the first version of the Unix operating system to see wide release outside Bell Labs. It was released in May 1975 and, like its direct predecessor, targeted the DEC PDP-11 family of minicomputers. It was superseded by Version 7 Unix in 1978/1979, although V6 systems remained in regular operation until at least 1985.
At this time, the developers of the Programmer's Workbench UNIX distribution, most notably John Mashey, began modifying the Thompson shell to make it more suitable for programming.The result, known as the PWB shell or the Mashey shell, included more advanced flow-control mechanisms and introduced shell variables, but remained limited by the necessity to remain compatible with the Thompson shell.
The Programmer's Workbench (PWB/UNIX) is an early, now discontinued, version of the Unix operating system created in the Bell Labs Computer Science Research Group of AT&T. Its stated goal was to provide a time-sharing working environment for large groups of programmers, writing software for larger batch processing computers.
John R. Mashey is a US computer scientist, director and entrepreneur.
The PWB shell was a Unix shell.
Finally, the Thompson shell was replaced as the main Unix shell by the Bourne shell in Version 7 Unix and the C shell in 2BSD, both released in 1979. Since virtually all modern Unix and Unix-like systems are descended from V7 and 2BSD, the Thompson shell is generally no longer used. It is, however, available as open-source as part of several Ancient Unix source distributions, and has been ported to modern Unices as a historical exhibit.
Bash is a Unix shell and command language written by Brian Fox for the GNU Project as a free software replacement for the Bourne shell. First released in 1989, it has been used widely as the default login shell for most Linux distributions and Apple's macOS Mojave and earlier versions. A version is also available for Windows 10. It is also the default user shell in Solaris 11.
sed is a Unix utility that parses and transforms text, using a simple, compact programming language. sed was developed from 1973 to 1974 by Lee E. McMahon of Bell Labs, and is available today for most operating systems. sed was based on the scripting features of the interactive editor ed and the earlier qed. sed was one of the earliest tools to support regular expressions, and remains in use for text processing, most notably with the substitution command. Popular alternative tools for plaintext string manipulation and "stream editing" include AWK and Perl.
A shell script is a computer program designed to be run by the Unix shell, a command-line interpreter. The various dialects of shell scripts are considered to be scripting languages. Typical operations performed by shell scripts include file manipulation, program execution, and printing text. A script which sets up the environment, runs the program, and does any necessary cleanup, logging, etc. is called a wrapper.
The Bourne shell (
sh) is a shell, or command-line interpreter, for computer operating systems.
ls is a command to list computer files in Unix and Unix-like operating systems.
ls is specified by POSIX and the Single UNIX Specification. When invoked without any arguments, ls lists the files in the current working directory. The command is also available in the EFI shell. In other environments, such as DOS, OS/2, and Microsoft Windows, similar functionality is provided by the
dir command. The numerical computing environments MATLAB and GNU Octave include an
ls function with similar functionality.
rc is the command line interpreter for Version 10 Unix and Plan 9 from Bell Labs operating systems. It resembles the Bourne shell, but its syntax is somewhat simpler. It was created by Tom Duff, who is better known for an unusual C programming language construct.
In computer programming, standard streams are preconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin), standard output (stdout) and standard error (stderr). Originally I/O happened via a physically connected system console, but standard streams abstract this. When a command is executed via an interactive shell, the streams are typically connected to the text terminal on which the shell is running, but can be changed with redirection or a pipeline. More generally, a child process inherits the standard streams of its parent process.
Seventh Edition Unix, also called Version 7 Unix, Version 7 or just V7, was an important early release of the Unix operating system. V7, released in 1979, was the last Bell Laboratories release to see widespread distribution before the commercialization of Unix by AT&T Corporation in the early 1980s. V7 was originally developed for Digital Equipment Corporation's PDP-11 minicomputers and was later ported to other platforms.
In computing, redirection is a form of interprocess communication, and is a function common to most command-line interpreters, including the various Unix shells that can redirect standard streams to user-specified locations.
In computing, tee is a command in command-line interpreters (shells) using standard streams which reads standard input and writes it to both standard output and one or more files, effectively duplicating its input. It is primarily used in conjunction with pipes and filters. The command is named after the T-splitter used in plumbing.
In computing, a shebang is the character sequence consisting of the characters number sign and exclamation mark at the beginning of a script. It is also called sha-bang, hashbang, pound-bang, or hash-pling.
sum is a core utility available on Unix and Unix-like operating systems. This utility outputs the checksum of each argument file, as well as the number of blocks they take on disk.
The script command is a Unix utility that records a terminal session. The scriptreplay command offers a replay function to script. The session is captured in file name typescript by default; to specify a different filename follow the script command with a space and the filename as such: script recorded_session.
In computing, process substitution is a form of inter-process communication that allows the input or output of a command to appear as a file. The command is substituted in-line, where a file name would normally occur, by the command shell. This allows programs that normally only accept files to directly read from or write to another program.
cat is a standard Unix utility that reads files sequentially, writing them to standard output. The name is derived from its function to concatenate files.