Re: How to choose the shell?

[Paul Smith]

On Sun, 2021-09-05 at 20:15 +0300, Eli Zaretskii wrote:
> But the way we build the batch file assumes cmd.exe, because we have
> no idea how to write scripts for other programs that can be used as
> "shells".  Also, we have no idea about the quoting used by other
> shells, so the tests that decide to "goto slow" due to fancy quoting
> are also prone to fail.

I'm not sure I understand.

Clearly if SHELL is not changed then we need to do whatever is
necessary to get the default shell (sh or cmd) to work.  I understand
that this involves more complexity with cmd than sh.

But if the user changes SHELL to something that's not known to make
then it's up to the user to make that work.  In that situation we
should simply pass along the expanded recipe lines as they are written
in the makefile, using the value of SHELL as the command and the value
of .SHELLFLAGS as the flags.  It's up to the user to make sure it works
with their customized setup, it's not something GNU make can do
anything about.  So it shouldn't try.

Perhaps there's a good argument to be made, in 2021 with PowerShell
ubiquitous on Windows system and also available on non-Windows systems,
that we should teach GNU make how to use PowerShell as an optional
"builtin shell" so that if the user sets SHELL to PowerShell we can
handle that properly.  But that's just another special case; we need to
solve the general case as well.

It's also possible that generalizing the batch file model of command
invocation would be good; there are situations even in GNU/Linux, which
has far higher limits than Windows, where providing an entire command
as a single argument causes exec to fail by exceeding limits.  We have
SHELL and .SHELLFLAGS.  Maybe adding a new variable like .SHELLARG that
controlled the format of the argument somehow (either the command
string, which would be the default, or some way to write it to a
temporary file and pass that file to the SHELL) would be useful.