| Developer(s) | Kenneth Almquist |
|---|---|
| Initial release | May 30, 1989 |
| Written in | C |
| Operating system | Unix-like |
| Platform | Cross-platform |
| Type | Unix shell |
| Website | www |
Almquist shell (also known as A Shell, ash and sh) is a lightweight Unix shell originally written by Kenneth Almquist in the late 1980s. Initially a clone of the System V.4 variant of the Bourne shell, it replaced the original Bourne shell in the BSD versions of Unix released in the early 1990s.
ash was first released via a posting to the comp.sources.unix Usenet news group, approved and moderated by Rich Salz on 30 May 1989. It was described as "a reimplementation of the System V shell [with] most features of that shell, plus some additions". [1]
Fast, small, and virtually compatible[ citation needed ] with the POSIX standard's specification of the Unix shell, ash did not provide line editing or command history mechanisms, because Almquist felt that such functionality should be moved into the terminal driver. However, current variants support it.
The following is extracted from the ash package information from Slackware v14:
ash (Kenneth Almquist's ash shell)
A lightweight (92K) Bourne compatible shell. Great for machines with low memory, but does not provide all the extras of shells like bash, tcsh, and zsh. Runs most shell scripts compatible with the Bourne shell. Note that under Linux, most scripts seem to use at least some bash-specific syntax. The Slackware setup scripts are a notable exception, since ash is the shell used on the install disks. NetBSD uses ash as its /bin/sh.
Myriad forks have been produced from the original ash release. [2] These derivatives of ash are installed as the default shell (/bin/sh) on FreeBSD, NetBSD, DragonFly BSD, MINIX, and in some Linux distributions. MINIX 3.2 used the original ash version, whose test feature differed from POSIX. [3] That version of the shell was replaced in MINIX 3.3. Android used ash until Android 4.0, at which point it switched to mksh. [4]
| Developer(s) | Herbert Xu |
|---|---|
| Initial release | July 15, 1997 |
| Written in | C |
| Operating system | Linux, Android |
| Type | Unix shell |
| License | 3-clause BSD license with mksignames under GNU GPL [5] |
| Website | gondor |
In 1997 Herbert Xu ported ash from NetBSD to Debian Linux. In September 2002, with release 0.4.1, this port was renamed to Dash (Debian Almquist shell). Xu's main priorities are POSIX conformance and slim implementation. [2]
Like its predecessor, Dash implements support for neither internationalization and localization nor multi-byte character encoding (both required in POSIX).[ citation needed ] Line editing and history support based on GNU Readline is optional (--with-libedit).
Because of its slimness, Ubuntu decided to adopt Dash as the default /bin/sh [6] [7] in 2006. The reason for using Dash is faster shell script execution, [8] especially during startup of the operating system, compared to previous versions of Debian and Ubuntu that used Bash for this purpose, although Bash is still the default login shell for interactive use. [9] Dash became the default /bin/sh in Ubuntu starting with the 6.10 release in October 2006. [7] Dash replaced Bash and became the default /bin/sh in Debian 6 (Squeeze). [6]
A result of the shift is that many shell scripts were found making use of Bash-specific functionalities ("bashisms") without properly declaring it in the shebang line. [10] [11] The problem was first spotted in Ubuntu and the Ubuntu maintainers decided to make all the scripts comply with the POSIX standard. The changes were later upstreamed to Debian, which soon adopted Dash as its default /bin/sh too. As a result, all /bin/sh scripts in Debian and Ubuntu are guaranteed to be POSIX-compliant, save for the extensions merged into Dash for convenience (local, echo -n, test -a / -o). [12] [13] A similar transition has happened in Slackware Linux, although their version of ash is only partially based on Dash. [2]
Ash (mainly the Dash fork) is also fairly popular in embedded Linux systems. Dash version 0.3.8-5 was incorporated into BusyBox, the catch-all executable often employed in this area, and is used in distributions like DSLinux, Alpine Linux, Tiny Core Linux and Linux-based router firmware such as OpenWrt, Tomato and DD-WRT.
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. The shell's name is an acronym for Bourne Again Shell, a pun on the name of the Bourne shell that it replaces and the notion of being "born again". First released in 1989, it has been used as the default login shell for most Linux distributions and it was one of the first programs Linus Torvalds ported to Linux, alongside GCC. A version is also available for Windows 10 and Windows 11 via the Windows Subsystem for Linux. It is also the default user shell in Solaris 11. Bash was also the default shell in BeOS, and in versions of Apple macOS from 10.3 to 10.15, which changed the default shell to zsh, although Bash remains available as an alternative shell.
KornShell (ksh) is a Unix shell which was developed by David Korn at Bell Labs in the early 1980s and announced at USENIX on July 14, 1983. The initial development was based on Bourne shell source code. Other early contributors were Bell Labs developers Mike Veach and Pat Sullivan, who wrote the Emacs and vi-style line editing modes' code, respectively. KornShell is backward-compatible with the Bourne shell and includes many features of the C shell, inspired by the requests of Bell Labs users.
A shell script is a computer program designed to be run by a 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 or logging, is called a wrapper.
The Single UNIX Specification (SUS) is a standard for computer operating systems, compliance with which is required to qualify for using the "UNIX" trademark. The standard specifies programming interfaces for the C language, a command-line shell, and user commands. The core specifications of the SUS known as Base Specifications are developed and maintained by the Austin Group, which is a joint working group of IEEE, ISO/IEC JTC 1/SC 22/WG 15 and The Open Group. If an operating system is submitted to The Open Group for certification, and passes conformance tests, then it is deemed to be compliant with a UNIX standard such as UNIX 98 or UNIX 03.
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.
The Bourne shell (sh) is a shell command-line interpreter for computer operating systems.
The C shell is a Unix shell created by Bill Joy while he was a graduate student at University of California, Berkeley in the late 1970s. It has been widely distributed, beginning with the 2BSD release of the Berkeley Software Distribution (BSD) which Joy first distributed in 1978. Other early contributors to the ideas or the code were Michael Ubell, Eric Allman, Mike O'Brien and Jim Kulp.
tcsh is a Unix shell based on and backward compatible with the C shell (csh).
In Unix-like and some other operating systems, the pwd command writes the full pathname of the current working directory to the standard output.
In the Unix operating system, shar is an archive format created with the Unix shar utility. A shar file is a type of self-extracting archive, because it is a valid shell script, and executing it will recreate the files. To extract the files, only the standard Unix Bourne shell sh is usually required.
The file command is a standard program of Unix and Unix-like operating systems for recognizing the type of data contained in a computer file.
A command shell is a command-line interface to interact with and manipulate a computer's operating system.
env is a shell command for Unix and Unix-like operating systems. It is used to either print a list of environment variables or run another utility in an altered environment without having to modify the currently existing environment. Using env, variables may be added or removed, and existing variables may be changed by assigning new values to them.
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 sharp-exclamation, sha-bang, hashbang, pound-bang, or hash-pling.
getopts is a built-in Unix shell command for parsing command-line arguments. It is designed to process command line arguments that follow the POSIX Utility Syntax Guidelines, based on the C interface of getopt.
The script command is a Unix utility that records a terminal session. It dates back to the 1979 3.0 BSD.
A Unix-like operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-like application is one that behaves like the corresponding Unix command or shell. Although there are general philosophies for Unix design, there is no technical standard defining the term, and opinions can differ about the degree to which a particular operating system or application is Unix-like.
mandoc is a utility used for formatting man pages in BSD Operating Systems, specifically those written in the mdoc and man macro languages. Unlike the groff and older troff and nroff tools that are predominantly used for this purpose by tools such as man, mandoc focuses specifically on manuals and is not suitable for general-purpose type-setting.