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Bourne shell
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see
Bourne shell
The '''Bourne shell''', or '''sh''', was the default
Unix shell of
Version 7 Unix Unix Version 7, and replaced the
Thompson shell, whose executable file had the same name, '''sh'''. It was developed by
Stephen Bourne, of
AT&T Bell Laboratories, and was released in 1977 in the
Version 7 Unix release distributed to colleges and universities. It remains a popular default shell for Unix accounts. The
Binary and text files binary program of the Bourne shell or a compatible program is located at /bin/sh on most
Unix systems, and is still the default shell for the root
superuser on many current Unix implementations.
= Origins =
Among the main goals of the Bourne shell was to take advantage of two key features of
Version 7 kernel:
* the much larger parameter (argument) lists, previously limited to 127 bytes and limited to 8192 bytes in Version 7.
* environment variables. These were a new feature of Version 7 and allowed a good deal of ancillary information to be passed to programs upon startup.
= Notable features =
The Bourne shell also was the first to feature the convention of using
File descriptor file descriptor 2 for
error messages, allowing much greater programmatic control during scripting by keeping error messages separate from data.
Although it is used as an interactive command interpreter, it was always intended as a
scripting programming language scripting language. It gained popularity with the publication of ''The UNIX Programming Environment'' by
Brian W. Kernighan and
Rob Pike. This was the first commercially published book that presented the shell as a programming language in a tutorial form.
Over the years, the Bourne shell was enhanced at AT&T. The various variants are thus called like the respective AT&T Unix version it was released with (some important variants being Version7, SystemIII, SVR2, SVR3, SVR4). As the shell was never versioned, the only way to identify it was testing its features.
Stephen Bourne carried into this shell some aspects of the
ALGOL 68C Compiler that he had been working on at
University of Cambridge Cambridge University. Notably he reused
ALGOL 68's "
if ~ then ~ else ~ fi", "
case ~ in ~ out ~ esac" and "
for ~ while ~ do ~ od" clauses in the common
Unix Bourne shell. Moreover - although the v7 shell is written in
C programming language C - Bourne took advantage of some
macros to give the C
source code an ALGOL 68 flavor.
= Decendents =
The
C shell (csh) was distributed with 4.1BSD, and took advantage of ''
job control'' features of the
BSD kernel. Job control is the ability to stop a program interactively and then restart it later. It was for this reason that the C shell gained popularity as a command interpreter. The C shell used a more "
C programming language C like" syntax for its programming features that was incompatible with the Bourne shell and purportedly an improvement.
The
Korn shell (ksh) written much later by
David Korn, was a middle road between these two shells, with syntax chiefly drawn from the Bourne shell and job control features drawn from the C shell.
Bash, also known as the ''Bourne-Again shell'', was later developed for the
GNU GNU project and takes features from the Bourne shell, csh and ksh.
Kenneth Almquist developed a clone of the Bourne Shell, known as the
Almquist Shell, which is in use today.
= Usage =
The
Bourne shell is now standard on all current
unix systems, although historically
BSD based systems had many scripts written in
csh. Bourne shell scripts can typically be run with
bash on
Linux.
After Sun released their
OpenSolaris variant of the
Bourne shell as
Open Source, a port of this shell for free Unix flavours (interesting concerning portability and historic interests) has been made available by the [http://heirloom.sourceforge.net/sh.html Heirloom project].
The original inspiration of the '''International Obfuscated
C_programming_language C Code Contest''' (
IOCCC - which is a contest of worst coding practices) came from the
Bourne Shell source and the
Finger_protocol finger command as distributed in Unix version
4.2BSD.
=External links=
Category:Domain-specific programming languages
Category:Text-oriented programming languages
Category:Scripting languages
Category:Unix shells
Category:Unix software
Category:POSIX standards
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