Re: avoid wrapper scripts when possible

[Hartmut Goebel <h.goebel@crazy-compilers.com>]

Hallo Ricardo,

Am 02.11.2017 um 22:31 schrieb Ricardo Wurmus:
> This made me wonder if we could avoid shell wrappers in more cases.

This is an interesting challenge :-)

> If
> the target script is a Python script we could set the environment
> variables right after the Python shebang with Python code.  If the
> target script is a shell script we can set environment variables right
> there after the shebang.

Basically thsi would be a good solution IMO. But I'm afraid it might be
complicated to insert the code "right after the […] shebang". For
example Python has "doc-strings" [1], this is: if the first statement of
the script is a string (expression statement), this string is put into
the variable __doc__. So for at least for Python we might need a
language-aware scanner to insert the code at the correct position. We
might need similar tor other languages.

But taking your challenge :-) I had another idea which should work for
all script languages:

The real script's she-bang delegates to the wrapper (instead of
/bin/sh), which execs "interpreter $0". Here is a proof on concept:

....8<------- real.py
#!/tmp/wrapper.sh
print("This is real")
import sys, os
print("sys.path[:2]", sys.path[:2])
print("argumentes:", sys.argv)
print("ppid", os.getppid())
....8<-------

....8<-------  wrapper.sh
#!/bin/sh
echo "This is the wrapper"
echo "arguments in wrapper:" "$@"
echo "ppid:" $PPID
export PYTHONPATH=/foo/bar
exec python3 /tmp/real.py "${@:2}" # <- replace first argument by full path
....8<-------

I have to admit that this still adds another script and is less elegant,
but should be easier to implement.

[]1] https://www.python.org/dev/peps/pep-0257/#what-is-a-docstring

-- 
Regards
Hartmut Goebel

| Hartmut Goebel          | h.goebel@crazy-compilers.com               |
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