[sf-lug] 'source' works but 'shebang' doesn't

[jim]

(wild applaurs!)


On 08/26/2016 06:44 PM, Akkana Peck wrote:
> Alex Kleider writes:
>> Mystery:
>>
>> alex at X301n3:~/Py/Backup/Backup$ cat ./path.sh
>> #!/bin/bash
>> # Add current working directory to the PYTHONPATH.
>> export PYTHONPATH="${PYTHONPATH:+$PYTHONPATH:}$(pwd)"
> [ ... ]
>> I don't understand how
>> source ./path.sh
>> does the job but
>> ./path.sh
>> does not!
>>
>> Can anyone explain?
> It is working -- just not the way you expect.
>
> When you run ./path.sh, it looks at the shebang and runs the shell
> you specify there -- as a subshell of the one you're typing in. That
> subshell reads the lines of the script and exports PYTHONPATH in
> that subshell, and when it's done reading the script, it exits,
> leaving you in your original shell, which still has its original
> environment.
>
> When you source ./path.sh, "source" explicitly tells your current
> shell to run the commands in the script *in the current shell*.
> So this time, export modifies your current shell rather than
> executing a subshell.
>
> Source also ignores the shebang line, since you've explicitly told
> it you want your current shell to execute it, not some other
> program. Even if you have a shebang line that says something like
> #!/usr/bin/env python, with source your shell will try to execute it
> as a shell script. Try it! It's especially amusing if your python
> program starts with import lines: I'll leave the question of what
> it's doing in that case as a fun exercise for the reader.
>
>          ...Akkana
>
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