Re: 01/01: services: Add ‘/usr/bin/env’ special file.

[Jesse Gibbons <jgibbons2357@gmail.com>]

Hello,
On Sun, 2019-09-08 at 23:48 +0200, Ludovic Courtès wrote:
> Hi,
> 
> Jesse Gibbons <jgibbons2357@gmail.com> skribis:
> 
> > If I might chip in here to try to make this discussion a little
> > more
> > productive, a user suggested /usr/bin/env should be added by
> > default[0]
> > to solve a problem[1]. In summary, the user wanted to have a
> > standard
> > for scripting in guile and other common GNU distros. If including
> > /usr/bin/env by default is not the best solution to the problem,
> > perhaps we can find a better solution.
> > 
> > I suggest we add the "guix shebang" command, which takes a script
> > and
> > returns a script with a shebang pointing to the proper source, like
> > what 'patch-shebangs build phase does to all the scripts in the
> > build
> > source. It could replace the input script (perhaps when given the
> > --
> > replace option) or it could put the resulting script in the store
> > and
> > accept the --root= option.
> 
> Would “guix shebang” modify the script, or would it be used as the
> shebang?
I suppose it could work either way. Since the scripts are intended to
be modified by the audience[1], it would be easier to have a command to
run as little as possible. On GuixSD, that would be as often as "guix
pull && guix upgrade" updates the program that runs the script; on
other systems it would be unnecessary. So modifying the script itself
would make the process simpler.

[1]https://lists.gnu.org/archive/html/help-guix/2019-09/msg00001.html
> 
> Either way, I’m not sure it’d really solve the initial use case very
> well (the initial request was to be able to run scripts unmodified,
> AIUI.)
I see two solutions to the problem:
1. Run the scripts unmodified (ideal). This can only be accomplished if
the shebang can rely on a program in a standard location (i.e.
/usr/bin/env). Adding /usr/bin/env by default currently is up for
debate in this thread.

2. Patch the shebang with a command that can be run as rarely as
possible, ideally only once. If we keep /usr/bin/env out of %standard-
services or %de then this is the last solution I can think of. It could
be an inline awk or sed script (like the scripts throughout LFS), which
would have to be pulled out every time a user has new script, or a guix
command which would always be available to all users with this
particular problem. Guix package is an immediate choice, but was
rejected because it would make things more commplicated[1], not to
mention simpler scripts are probably shorter than a package definition.
The simplest solution here would be something like "guix shebang".

[1] https://lists.gnu.org/archive/html/help-guix/2019-09/msg00001.html

I have no preference which solution is used, but if /usr/bin/env is not
available in a build environment, and we can find a way to detect calls
to programs in standard locations and patch them when we build them, I
know of no reason not to include /usr/bin/env by default.

If anyone has a fourth solution, I would love to see it.

> Thanks,
> Ludo’.

-- 
-Jesse