How to go back to bash (from dash)?

Magnus Therning magnus at
Fri Oct 14 09:08:46 UTC 2005

On Fri, Oct 14, 2005 at 01:01:57PM +0700, Ali Milis wrote:
>Magnus Therning wrote:
>> >May I know, how to return to bash as  /bin/sh (from dash)?
>> >Why it is not in /etc/alternatives?
>> $ sudo dpkg-reconfigure dash
>> Then you'll be asked if you want dash to be /bin/sh. Answer "no" and you
>> revert to having bash as /bin/sh.
>Thank you! May I know what was behind introducing POSIX's "dash"?
>Many bash scripts break if using dash  B-(
>And is there any specific reason not using /etc/alternatives?

All good questions. :-) Don't take my answers as authoritative, I'm just
making this up as I go ;-)

I imagine one could argue that shell scripts that start with


should be POSIX shell compatible. I.e. they should work under any POSIX
compliant shell (bash, dash, ksh, zsh, ...). If you need some non-POSIX
extension then you should explicitly use the desired shell, e.g.


It's a little unfortunate that invoking bash as `sh` only turns on
POSIX-compliant startup behaviour, it doesn't disable bash's non-POSIX
extensions. (This is based on what I've read in the man-page, and it
seems to be supported by your statements as well.) So, in short, using
bash-isms in a shell script that starts with


results in bugs.


Magnus Therning                    (OpenPGP: 0xAB4DFBA4)
magnus at

Software is not manufactured, it is something you write and publish.
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