The Debian Almquist shell (dash) is a Unix shell

Unix shell

A Unix shell is a command-line interpreter or shell that provides a traditional user interface for the Unix operating system and for Unix-like systems...

, much smaller than bash but still aiming at POSIX

POSIX

POSIX , an acronym for "Portable Operating System Interface", is a family of standards specified by the IEEE for maintaining compatibility between operating systems...

-compliancy. It requires less disk space but is also less feature-rich.

History

Dash is a direct descendant of the NetBSD

NetBSD

NetBSD is a freely available open source version of the Berkeley Software Distribution Unix operating system. It was the second open source BSD descendant to be formally released, after 386BSD, and continues to be actively developed. The NetBSD project is primarily focused on high quality design,...

 version of the Almquist shell (ash). It was ported to Linux

Linux

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

 by Herbert Xu in early 1997. It was renamed to dash in 2002.

Dash, like ash, executes shell script

Shell script

A shell script is a script written for the shell, or command line interpreter, of an operating system. It is often considered a simple domain-specific programming language...

s faster than bash and depends on fewer libraries. It is believed to be more reliable in the case of upgrade problems or disk failures. dash may be used as a:

• shell on installation floppy disk
  Floppy disk
  A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...
  
  s
• root user shell
• /bin/sh replacement
• testing environment for shell scripts to verify their compatibility with POSIX syntax

Dash is a modern replacement for ash in Debian

Debian

Debian is a computer operating system composed of software packages released as free and open source software primarily under the GNU General Public License along with other free software licenses. Debian GNU/Linux, which includes the GNU OS tools and Linux kernel, is a popular and influential...

 and was expected to be the default /bin/sh for Debian Lenny. Dash has been the default /bin/sh in Ubuntu

Ubuntu (operating system)

Ubuntu is a computer operating system based on the Debian Linux distribution and distributed as free and open source software. It is named after the Southern African philosophy of Ubuntu...

 since the 6.10 release in October 2006. During the transition by Ubuntu, numerous scripts making use of Bash-specific functionality (but not declaring it) were discovered. To avoid errors, Bash-specific scripts can be modified to be compatible with the appropriate standard, or explicitly declare their use of bashisms by explicitly setting the interpreter to bash via the shebang

Shebang (Unix)

In computing, a shebang is the character sequence consisting of the characters number sign and exclamation point , when it occurs as the first two characters on the first line of a text file...

line: #!/usr/bin/env bash.

External links

• Dash home
• Debian package overview
• Debian bugs tagged goal-dash
• Dash as default /bin/sh in Debian, Ubuntu
• Dash mailing list archive
• Shells in Debian