[Slackbuilds-users] bashisms?

[John Vogel]

On Wed, 2 Sep 2015 17:09:45 +0200
Andrzej Telszewski <atelszewski at gmail.com> wrote:

> On 02/09/15 16:51, John Vogel wrote:
> > On Wed, 2 Sep 2015 15:52:30 +0200
> > Andrzej Telszewski <atelszewski at gmail.com> wrote:
> >
> >> Hi,
> >>
> >> Today I was writing code to execute script from C code and I'd like to
> >> share with you what I've found. It stroke me, but should otherwise be
> >> obvious.
> >>
> >> It seems that shebang has only meaning if the script is invoked
> >> directly, that is:
> >> $ ./whatever.SlackBuild
> >> or
> >> $ sh -c ./whatever.SlackBuild
> >>
> >> otherwise, shebang is nothing more than a comment...
> >>
> >> If you run your script through sh (which links to bash), it doesn't
> >> matter what the shebang is, it can be #!/bin/csh, and the script is
> >> still going to be interpreted by sh.
> >>
> >> This might be important, as sbopkg uses sh to execute the build.
> >>
> >> --
> >> Best regards,
> >> Andrzej Telszewski
> >
> > Are you sure? I tried to test this using the following script
> > (executable bit is set):
> >
> 
> Yes, I'm sure;)
> 
> > -- start ./test_script
> > #!/bin/bash
> > printf '$0=%s\n' "$0"
> > printf 'BASH_VERSION=%s' "$BASH_VERSION"
> > -- end ./test_script
> >
> > When run by all the shells I have (ash,bash,dash,ksh,mksh,tcsh),
> > they all output the same. I used the following loop to run
> > the commands:
> >
> > for s in ash bash dash ksh mksh tcsh sh csh ; do
> > /bin/$s -c ./test_script
> > done
> 
> That's it.  If you use -c switch, then the script is executed as if you 
> used ./, that is, the shebang is processed.  Try running your test 
> without the -c switch and placing some constructs that are only 
> understood by one of the shells.
> 
> $ sh -c ./whatever.SalckBuild
> is equivalent to:
> $ ./whatever.SalckBuild
> 
> but
> 
> $ sh ./whatever.SalckBuild
> will process the script by whichever shell is linked to the sh, without 
> taking into account the shebang (maybe there are shells, that upon 
> seeing shebang in the first line don't treat it as comment, but I don't 
> know about it).
> 
> >
> > The output for each is identical:
> > $0=./test_script
> > BASH_VERSION=4.3.39(1)-release
> >
> > But if I change the shebang line to '#!/bin/dash', then the
> > output for all is:
> > $0=./test_script
> > BASH_VERSION=
> >
> > At the time of running this /bin/sh -> /bin/bash. Changing
> > /bin/sh to point anything else (other than tcsh/csh, I never
> > set /bin/sh to a c shell) did not change the results.
> >
> > I'm sure I could carry this testing further, but I think
> > the point might be proved well enough. I didn't want to
> > step into this discussion, as I have rather conservative
> > opinion about proper use of shebang and would rather not
> > go down this road here. But let's keep things accurate,
> > as far as how things actually work.
> >
> > John

> -- 
> Best regards,
> Andrzej Telszewski

Yes, indeed. Fair enough. I think I misread your first post
wrong to mean the opposite. My apologies if I came off a bit
harsh. You make a good point.

Cheers,
John