Re: "shell" in Makefile

On Sun, Jun 24, 2007 at 09:40:40AM -0700, Easthope wrote:
> Debian users,
>
> In
>
> http://git.kernel.org/?p=linux/kernel/git/linville/wireless-dev.git;a=
> summary
>
> Vivek described a makefile containing this text.
>
> obj-m := hello.o
> KDIR := /lib/modules/$(shell uname -r)/build
> PWD := $(shell pwd)
> default:
> $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
>
> shell is not a command in the Etch here.

It is not a command in etch. But it is in GNU Make:

    http://www.gnu.org/software/make/manual/html_node/Shell-Function.html#Shell-Function

> So what is "shell uname -r" and "shell pwd"?

That's the way to get the output a command into a Make variable.

> Why not just $(uname -r) and $(pwd)?

It would be in bash - where $( somecommand ) is replaced by the output of somecommand.

Make uses the syntax of $(variablename) to reference the value of a variable - and $(functionname params) to call functions - one of which is 'shell', which calls an external (to make) command.

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Hope this helps

-- 
Karl E. Jorgensen
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