running a simple command line tool

[Avi Greenbury]

CJ Tres wrote:
> On 02/23/2012 05:40 AM, Avi Greenbury wrote:
> > CJ Tres wrote:
> >
> >> Running basic smoketest.
> >> smoketest.sh: 12: [[: not found
> >> smoketest.sh: 18: [[: not found
> >> smoketest.sh: 26: function: not found
> >> Error found.  Leaving run.11199 in place.
> >> Unable to execute command: 'sh test.sh'
> >
> > This looks like it's down to a naughty developer :)
> >
> > [[ is a 'bashism' (so-called because it's something that exists in
> > bash but not in the 'sh' that it's a development from).
> >
> > The command 'sh test.sh' passes the 'test.sh' script to 'sh' which
> > is a shell. Normally and historically it's a link to /bin/bash but
> > modern Ubuntus and Debians use dash instead (in the interests of
> > speed). [[ doesn't work in dash, so the test script fails on that
> > error and the install aborts.
> 
> 
> Running echo $SHELL returns /bin/bash on this install - Natty.

Yeah, that's the default shell for your user. /bin/bash should always
be bash, the iffy bit is where /bin/sh goes. It used to go to the
bourne shell, before bash (the 'bourne again' shell, it's successor)
was written. After that, it became common to make /bin/sh simply a link
to /bin/bash since bash's features are a superset of the bourne shell's
- something expecting the bourne shell will work in bash.

A few releases of Debian (and so Ubuntu) ago, it was agreed
that /bin/sh would instead be a link to dash, which is a good deal
smaller than bash. It's still a superset of the bourne shell, so
anything that only requires the bourne shell will still work, but it's
a different, and smaller, superset than bash. 

The problem is that a lot of people had come to assume that /bin/sh was
bash, not the bourne shell, and when you try to run something that's
got bashisms that are not present in dash (like the '[[' construct) in
dash you get a syntax error.

The error message tells you what command was run: 
  Unable to execute command: 'sh test.sh'

So, we can find out what's run when we execute 'sh':
root at donkey:~# which sh
/bin/sh
root at donkey:~# ls -l /bin/sh
lrwxrwxrwx 1 root root 4 2011-05-03 16:04 /bin/sh -> dash
root at donkey:~# 

And you can see that it's a symlink to dash (that's what the '->' syntax
means - the fact it just says 'dash' means it's in the same directory,
so /bin/dash). 

Now, you *could* bodge it by repointing that symlink, but that's not a
great idea in case things call that expecting dashisms that aren't in
bash. What *should* happen is that when a script needs bash it is passed
to bash, not sh. This is something that should really be fixed in those
test scripts in that installer.

-- 
Avi