[sf-lug] glorious dash :-)

[Michael Paoli]

Yes, dash (Debian Almquist shell) is rather glorious. :-)

As I seem to recall it earlier described as a "minimally compliant POSIX
shell".  Well, it may be a slight bit more/bigger than that, but not by
much, and generally lacks most all the bloat (and bugs!) of bash.

E.g. even just to reasonably describe them in their man pages:

$ 2>>/dev/null man bash | col -b | expand | wc
    5742   44536  339409
$ 2>>/dev/null man dash | col -b | expand | wc
    1590   10121   74074
$
So, we see a rather large size difference right there.
And binaries?
$ ls -Lno /bin/[bd]ash
-rwxr-xr-x 1 0 1029624 Nov 12  2014 /bin/bash
-rwxr-xr-x 1 0  125400 Nov  8  2014 /bin/dash
$
A quite significant size difference ... and that's not even getting into
library dependencies.
$ ldd /bin/bash /bin/dash
/bin/bash:
         linux-vdso.so.1 (0x00007ffd81581000)
         libncurses.so.5 => /lib/x86_64-linux-gnu/libncurses.so.5  
(0x00007f0637252000)
         libtinfo.so.5 => /lib/x86_64-linux-gnu/libtinfo.so.5  
(0x00007f0637028000)
         libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f0636e24000)
         libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f0636a79000)
         /lib64/ld-linux-x86-64.so.2 (0x00007f0637477000)
/bin/dash:
         linux-vdso.so.1 (0x00007ffe1497c000)
         libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f6f0c423000)
         /lib64/ld-linux-x86-64.so.2 (0x00007f6f0c9ef000)
Those used by dash, are also used by bash,
but bash additionally uses these not used by dash:
         libncurses.so.5 => /lib/x86_64-linux-gnu/libncurses.so.5  
(0x00007f0637252000)
         libtinfo.so.5 => /lib/x86_64-linux-gnu/libtinfo.so.5  
(0x00007f0637028000)
         libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f0636e24000)
$ ls -Lno /lib/x86_64-linux-gnu/libncurses.so.5 \
> lib/x86_64-linux-gnu/libtinfo.so.5 /lib/x86_64-linux-gnu/libdl.so.2
-rw-r--r-- 1 0  14664 Feb 29 09:29 /lib/x86_64-linux-gnu/libdl.so.2
-rw-r--r-- 1 0 151120 Dec  8  2014 /lib/x86_64-linux-gnu/libncurses.so.5
-rw-r--r-- 1 0 171800 Dec  8  2014 /lib/x86_64-linux-gnu/libtinfo.so.5

Oh, and bash - also has bugs not present in dash and (most) other
shells:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=86397

If I'm writing a shell script, I generally prefer more standard,
smaller, fewer bugs, and less likely to break now, or in future.  The
dash shell is generally a much better fit for that than bash.  There's
darn good reasion it's used for /bin/sh on, e.g. Debian:
$ ls -on /bin/sh
lrwxrwxrwx 1 0 4 Nov  8  2014 /bin/sh -> dash
$ lsb_release -d
Description:    Debian GNU/Linux 8.5 (jessie)
$
It's also the provided or default shell on many operating systems.

references/excerpts:
https://packages.debian.org/jessie/dash
https://en.wikipedia.org/wiki/Almquist_shell
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=86397
http://buug.org/pipermail/buug/2011-August/003862.html
http://buug.org/pipermail/buug/2011-August/003866.html
http://buug.org/pipermail/buug/2011-August/003869.html
http://buug.org/pipermail/buug/2011-August/003871.html

> From: "Alex Kleider" <akleider at sonic.net>
> Subject: Re: [sf-lug] > and >> and < and << and |
> Date: Mon, 08 Aug 2016 18:29:02 -0700

> On 2016-08-08 10:32, jim wrote:
>
>> (The DASH man page is glorious, unlike some other
>> man pages.)
>
> I've noticed that some small (SoC) systems come with dash rather  
> than bash and assumed that the former was a 'smaller' version of the  
> latter and was surprised that my system (current LTS of Ubuntu)  
> seems to have both installed.
> $ man DASH  # man page
> $ man dash  # same man page
> $ man bash  # different structure but I find no differences in  
> behaviour described.
> $ dash # => a '$' prompt by itself; I'm in another shell, dash this time.
> $ DASH
> DASH: command not found
> $ bash  # a pause and then the same prompt returns; I'm in another shell.
>
> interesting.
> Under what circumstances would someone with both installed wish to  
> use dash rather than bash?