[GRASS-dev] Re: MS-Windows native GRASS

[Glynn Clements]

Michael Barton wrote:

> >> Can you give an example of how you need to run a bash script under windows?
> > 
> > If $cmd is a script, you need to explicitly specify the interpreter.
> > E.g.:
> > 
> > exec $cmd $arg1 $arg2
> > 
> > needs to be changed to:
> > 
> > exec sh $cmd $arg1 $arg2  # for a shell script
> > or:
> 
> This should go into the runandoutput.tcl procedures. Can this be used for
> all systems, or do I need to specify that this syntax is for mysys platforms
> only? env(HOSTTYPE)=???

The problem is: how do you know whether $cmd is a script or a binary
executable?

On Unix, it doesn't matter; you can execute scripts just like binary
executables.

For Windows, there are a couple of options:

1. Add extensions (.sh, .tcl etc) to scripts, ensure that the
appropriate interpreters are associated with those extensions, and add
those extensions to PATHEXT. Then, executing "foo" will look for
foo.sh and foo.tcl in addtion to foo.exe, foo.cmd etc. Adding the
extensions would have to be done only for Windows; we don't want to
have to type the extensions on Unix.

2. Create a wrapper for executing commands, which automatically
detects scripts and invokes the appropriate interpreter. Replace usage
of Tcl's exec/open commands with our own versions which invoke the
wrapper on Windows.

> > exec $env(GRASS_WISH) $cmd $arg1 $arg2 # for a Tcl/Tk script
> > etc.
> 
> Running a tcltk script from within tcltk shouldn't need this should it
> (i.e., from within a WISH environment)?

It does if you want to run it as a separate process, rather than
"source" it into the current wish process.

> Calling wish should only be
> necessary when starting a tcltk script from the command line or its
> equivalent in mysys, right?

MSys' bash autodetects scripts and invokes the interpreter
automatically. Cygwin's execve() behaves similarly.

It's only an issue if you are executing commands using the native
Windows calls, e.g. spawnl() or CreateProcess(), which is what Tcl's
exec/open commands will use for a native Windows version of Tcl/Tk.

> > Note that:
> > 
> > exec sh -c "$cmd $arg1 $arg2"
> > 
> > will work in some cases, but not all, so shouldn't be used.
> > 
> >> Sorry, but I don't quite get it yet. You suggest that this same syntax also
> >> runs under unix. Under Linux? Mac? I'm happy to test it on the Mac and at
> >> least a flavor or two of Linux.
> > 
> > It's unnecessary under Unix (including OSX); you can just execve() a
> > script, and the kernel will detect the #!/bin/sh and invoke /bin/sh
> > automatically.
> > 
> > This isn't the case on Windows. Unix emulation layers (e.g. Cygwin,
> > MinGW's bash) include specific code to detect scripts and invoke the
> > interpreter.
> 
> So it's an issue with mysys only?

Specifying the interpreter is only required for a native Windows
environment.

> Does it hurt to specify sh up front for
> ALL, or do we need to do this only for mysys platforms?

You only use "sh" for shell scripts, not binary executables or scripts
written in other languages.

-- 
Glynn Clements <glynn at gclements.plus.com>