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Change the default shell from an environment variable

From: Masahiro Yamada
Subject: Change the default shell from an environment variable
Date: Sun, 25 Jul 2021 23:51:48 +0900


GNU Make uses /bin/sh by default for
running recipe lines and $(shell ) functions.

You can change the shell by setting the
'SHELL' variable.

One note for this variable is that
SHELL is never set from the environment.
This is clearly documented [1].

The build system of a large project is often
divided into multiple sub-makes.
The top Makefile, and several sub-Makefiles.

Other variables can be set in the top
Makefile, and exported down to sub-makes.

For example:

export CC := gcc
export LD := ld
export OBJCOPY := objcopy

But, since it is not possible to propagate SHELL
down to sub-makes, we end up with adding the same setup:

   SHELL := /bin/bash

in every sub-makefiles.

So, here is one suggestion.

Does it make sense to add an environment variable
with  a less common name? It functions in the same
way as SHELL, but the difference is that it can be set
from the environment.

For example, 'MAKE_SHELL'.

In the top Makefile, you can do:

   export MAKE_SHELL := /bin/bash

then, GNU Make will use /bin/bash
not only in the top Makefile but also
in sub-makefiles.


Best Regards
Masahiro Yamada

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