[Slackbuilds-users] bashisms?

[Andrzej Telszewski]

On 02/09/15 17:13, John Vogel wrote:
> 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.

Well, I re-read my post and it should be me who should be sorry as I 
didn't explain it well enough;) I was very harsh;)

>
> Cheers,
> John
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