The Almquist shell (also known as A Shell, ash and sh) was originally Kenneth Almquist's clone of the SVR4-variant of the Bourne shell; it is a fast, small, POSIX-compatible Unix shell designed to replace the Bourne shell in later BSD distributions. Originally it did not feature line editing or command history mechanisms, because Almquist felt that such should be moved into the terminal driver; however, current variants support it.
Derivatives of ash are installed as the default shell (/bin/sh) on FreeBSD, NetBSD, DragonFly BSD, MINIX and Android. Ash is also fairly popular in embedded Linux systems; its code was incorporated into the BusyBox catch-all executable often employed in this area. Debian's version of ash is known as Debian Almquist Shell (dash).
Some Linux distributions also use a derivative of ash as the default shell, although Bash (Bourne Again Shell) is more popular. Debian and Ubuntu symlink /bin/sh to the dash shell for faster script execution, but keeps Bash as the default login shell.
Read more about Almquist Shell: History
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