What meaning of the ',' in ifneq ($(KERNELRELEASE),)

[fl]

Hi,
I am reading the following Makefile script. I do not understand the ',' in the ifneq clause. I do not find the explanation in a pdf book on 'make'. Could you explain it to me?


Thanks,



.....................
# If KERNELRELEASE is defined, we've been invoked from the
# kernel build system and can use its language.
ifneq ($(KERNELRELEASE),)
obj-m := hello.o
# Otherwise we were called directly from the command
# line; invoke the kernel build system.
else
KERNELDIR ?= /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
default:
$(MAKE) -C $(KERNELDIR) M=$(PWD) modules
endif

[Dan Espen]

fl <rxj...@gmail.com> writes:

> Hi,
> I am reading the following Makefile script. I do not understand the
> ,' in the ifneq clause. I do not find the explanation in a pdf book on
> make'. Could you explain it to me?

...
> ifneq ($(KERNELRELEASE),)

http://www.gnu.org/software/make/manual/html_node/Conditional-Syntax.html

Example of above shown.

--
Dan Espen

[bachchu...@gmail.com]

There are two arguments, one is $(KERNELRELEASE)& other is empty "".
Comma "," is just separating both.
ifneq is checking whether $(KERNELRELEASE) has empty value or not.

[neerajda...@gmail.com]

hi
iam new to device driver, here it is writtn that the if condition is used to check wheather the KERNELRELEASE has empty value or not but for what it is checking it

[Barry Margolin]

In article <b0a0f730-86c7-489f...@googlegroups.com>,

It's explained in the comment right before the test:

# If KERNELRELEASE is defined, we've been invoked from the
# kernel build system and can use its language.

--
Barry Margolin, bar...@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***