Re: strange behaviour of 'ifeq'

[Philip Guenther]

On Sun, Jun 21, 2009 at 1:48 PM, jacques<address@hidden> wrote:
> By writing a simple program (program_a), I was able to see some strange
> behaviours of 'ifeq'
>
> program_a:
> ifeq("foo","foo")  \
> TOOL = tool  \
> endif
>
> start:
>           @echo $TOOL
>
>
> whose execution by "make -f  program_a" yields a  newline.

"make -f program_a" tells make to ignore your Makefile and instead
read the file "program_a" as a Makefile.  Did you *really* do that, or
did you instead run
    make program_a
?

When I try "make program_a", I get the following:
$ make
make: Nothing to be done for `program_a'.
$


> First question: The gmake on-line manual states that the syntax of a
> conditional test follows the following template (7.2):
>
> conditional-directive
>    text-if-true
>    else
>    text-if-false
>    endif
>
> Notice that there is no backslash character in the definition. In
> 'program_a', if I don't put the backslashes, the program gives execution
> errors. So backslashes are compulsory eventhough the manual says otherwise.
> Is it just a bug that will be fixed in later versions or is there a deeper
> significance ( the 'ifdef' and 'ifndef' conditionals behave syntatically
> according to the gmakeon-line manual !!) ?

Where to start..

1) you did not actually write a ifeq conditional: to be an ifeq
conditional, there MUST
    be a space after the word "ifeq"!
2) ending a line with a backslash tells make to join the line with the
following line.
   By ending those two lines with backslashes, you effectively gave
make the following:

ifeq("foo","foo") TOOL = tool endif

That's a variable assignment!  Yes, the name of the variable is
  ifeq("foo","foo") TOOL

as can be confirmed by adding this to the 'start' target:
        @echo ${ifeq("foo","foo") TOOL}

You'll find that "make start" then echos "tool endif"

So: insert a space after 'ifeq' and remove the backslashes.


You'll then find that it still doesn't work...because you didn't use
the TOOL variable properly.  To make, "$TOOL" means "the value of the
'T' variable, followed by 'OOL'".  If a variable has more than one
character in it's name, you must enclose the name in either brackets
or parens.  Use ${TOOL} or $(TOOL).


I'm not sure what the "program_a" target is supposed to be doing in
your example Makefile.  You _do_ understand that the assignment to
TOOL will *not* be specific to that target, don't you?


Philip Guenther