Re: how to use a different /bin/sh with GNU Make?

[Tim Murphy]

Perhaps I can save Paul an explanation: running the shell has some
time cost so if the command looks simple enough then make executes it
without passing  to any shell.

On 13 October 2015 at 15:11, Mark Galeck <address@hidden> wrote:
> Thank you Paul!
>
> Well, the recipe I am using is the simplest possible recipe:
> all:    echo $(SHELL)
>
> OK, what do you mean by "runs the command directly rather than invoking a 
> shell"
>
> I tested that possibility (even though the manual clearly says that is not 
> the case).  I custom modified /bin/sh, then ran that, so that my 
> _current_shell_ was the modified one.  Then _in_that_context_ ran GNU Make 
> with the simple recipe.
> I had shell modified so that each time it interpreted a command, it would 
> print something to a log file.
> Nope.  When I ran GNU Make , the log file was not updated, so that meant, the 
> current modified shell, was not interpreting any command.
>
>       From: Paul Smith <address@hidden>
>  To: Mark Galeck <address@hidden>
> Cc: "address@hidden" <address@hidden>
>  Sent: Tuesday, October 13, 2015 5:02 AM
>  Subject: Re: how to use a different /bin/sh with GNU Make?
>
> On Tue, 2015-10-13 at 04:35 +0000, Mark Galeck wrote:
>> as root, I replaced the default /bin/sh with a shell compiled by me
>> with custom changes.  I expected GNU Make will use that shell by
>> default , but it does not - it still uses the original /bin/sh (which
>> was really bash) even though it is not there anymore.
>
> It would be very helpful if you provided an example of the recipe you're
> using.  Without that we can only speculate.
>
> GNU make contains a special "fast path" capability.  If it knows that
> the shell is a POSIX-compliant shell (because the shell is one of a set
> of known POSIX-compliant shells such as /bin/sh, /bin/bash, or others...
> for the complete list see the unix_shells[] array in the jobs.c file in
> the GNU make source code), and it determines that the recipe is "simple
> enough": it's a single command, has no IO redirection or pipes, the
> quoting is straightforward, and there are no shell variables in it, then
> make runs the command directly rather than invoking a shell.
>
> So for example, this recipe is run directly by make rather than starting
>
>
> a shell:
>
>   cc -Wall -o foo.o -c foo.c
>
> but this recipe would always start a shell:
>
>   cc -Wall -o foo.o -c foo.c; echo "Compilation complete"
>
> If you want to force make to always start a shell and never use the fast
> path the best way is to name your shell something else, like /bin/mgsh
> or something, then set make's SHELL variable to that path.  Since make
> is no longer sure if your shell is a POSIX shell, it will never use the
> fast path.
>
>
>
>
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