[Cialug] Tasks for learning shell scripting

[Don Ellis]

Yes, /bin/sh could be anything, and it's good to know what you're getting.

If it's zsh, it will behave differently depending on what name it's
called, and other shells may do something similar. Symbolic links (or
hard links) can be used to give a shell a different name.

The shells available for login are listed in /etc/shells

If you do an 'ls -l' on each of these, you can see which are symbolic
links to other locations, and which are the same binaries (maybe hard
links, maybe copies).

Example:
[11:40:09]:<ttys000>:donellis at MacRover.local:/etc
36 (536) $ ls -l /bin/*sh*
-rwxr-xr-x  1 root  wheel  1346544 Feb  4  2010 /bin/bash*
-rwxr-xr-x  2 root  wheel   767200 Feb 10  2010 /bin/csh*
-r-xr-xr-x  1 root  wheel  2186880 May 19  2009 /bin/ksh*
-r-xr-xr-x  1 root  wheel  1346624 Feb  4  2010 /bin/sh*
-rwxr-xr-x  2 root  wheel   767200 Feb 10  2010 /bin/tcsh*
-rwxr-xr-x  1 root  wheel  1597200 May 11  2009 /bin/zsh*

(I just did this in /bin because all the shells listed in my
/etc/shells are in /bin)

--Don Ellis


On Wed, Sep 29, 2010 at 11:37 AM, Matthew Nuzum <newz at bearfruit.org> wrote:
> On Wed, Sep 29, 2010 at 10:23 AM, Don Ellis <don.ellis at gmail.com> wrote:
>> Another thing, bash is often the default shell and ksh is an optional add-on.
>>
>> For a root login, sh is often used for the login shell because it is
>> on a filesystem that is mounted first, and doesn't depend on later
>> boot stages. However, for some systems, bash is used for root login,
>> since it is also on an initial filesystem. If a script might be run
>> before other filesystems are mounted, be sure the shell it runs in is
>> present when it's needed.
>
> Well, this gets to my point. /bin/sh could be anything. In Mac OS it's
> bash, in Ubuntu it's dash. What is it in other UNIX systems? Do most
> come with bash pre-installed? A few years ago GNU tools always had to
> be installed separately.
>
> Bash is such an awesome shell that once you grow accustomed to it you
> may have a hard time using others.
>
> I asked someone else and they suggested using bash and just making the
> student aware of the differences. This page actually explains it quite
> well: https://wiki.ubuntu.com/DashAsBinSh (Dash is a posix compliant
> shell focused on performance)
>
>
> --
> Matthew Nuzum
> newz2000 on freenode, skype, linkedin, identi.ca and twitter
>
> "An investment in knowledge pays the best interest." -Benjamin Franklin