The Debian Almquist shell (dash) is a Unix shell, much smaller than Bash, but it is still aiming at POSIX-compliance. It requires less disk space, but it is also less feature-rich.
Dash is a direct descendant of the NetBSD version of the Almquist shell (ash). It was ported to Linux by Herbert Xu in early 1997. It was renamed to dash in 2002.
Dash, like ash, executes shell scripts faster than Bash and depends on fewer libraries. Dash may be used as a:
- shell on installation floppy disks
- 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 and was expected to be the default /bin/sh for Debian Lenny  but actually became the default /bin/sh for Debian Squeeze. Dash has been the default /bin/sh in 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 line:
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