Proper shebang for python3

[Cameron Simpson]

On 21Jul2019 09:31, Chris Angelico <rosuav at gmail.com> wrote:
>On Sun, Jul 21, 2019 at 9:15 AM Cameron Simpson <cs at cskk.id.au> wrote:
>So.... you mean that a tool that depends on running on a consistent
>environment, it should use a shebang of "/usr/bin/python3.6" instead
>of "/usr/bin/env python3"?

Jeez. No. That is the _opposite_ of what I'm saying.

>Because, wow, that would be exactly what is
>already happening on my system. Why use /usr/bin/env and then wrap
>something around it to force the environment, when you could just set
>a correct shebang so it properly defines its execution environment?

Because the shebang is hardwired and inflexible.

Because it means hand patching (even scripted) a bazillion scripts to 
that they know their physical install.

Because it presumes detailed hardwired knowledge of the target system in 
a script which should work anywhere.

Instead a tiny _common_ shell script resembling this:

  #!/bin/sh
  # Run command in the official environment.
  exec env - PATH=/path/to/3.6venv/bin:/usr/sbin:/bin exec ${1+"$@"}

arranges things. The "env -" is aimed at "clean" daemon or install 
environments.  You can do subtler or less intrusive things in other 
settings.

There are any number of variations available here that don't hardwire 
the environment into the various _scripts_, but into the invocation 
setting. Or just start an environment (eg a shell) with the desired 
environment.

Cheers,
Cameron Simpson <cs at cskk.id.au>