dash 和 bash

1.

Bash is the shell, or command language interpreter, that will appear in the GNU operating system. Bash is an sh-compatible shell that incorporates useful features from the Korn shell (ksh) and C shell (csh).

http://www.gnu.org/s/bash/

Dash(Debian Almquist shell ) is a POSIX-compliant implementation of /bin/sh that aims to be as small as possible. It does this without sacrificing speed where possible. In fact, it is significantly faster than bash (the GNU Bourne-Again SHell) for most tasks.

2.

Ubuntu 的默认Shell是 Dash,

Bash 和 Dash两者语法是有区别的，详见

http://www.igigo.net/archives/169

例如

[ string1 = string2 ] 和 [ string1 == string2 ]

bash: 支持两者

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igi@gentoo ~ $ [ 'a' = 'a' ] && echo 'equal' equal igi@gentoo ~ $ [ 'a' == 'a' ] && echo 'equal' equal igi@gentoo ~ $ echo $0 /bin/bash

dash: 只支持=

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$ [ 'a' = 'a' ] && echo 'equal' equal $ [ 'a' == 'a' ] && echo 'equal' [: 2: a: unexpected operator $ echo $0 dash $

3.

如果Shell是从别的linux平台移植到Ubuntu, 应将 /bin/sh 改成bash