On Tue, 2023-02-28 at 19:02 -0600, Satish Balay via Bug reports and
discussion for GNU make wrote:
> This usage works with make-4.4 [and older versions] - but not 4.4.1
>
> balay@p1 /home/balay/tmp
> $ cat makefile
> all:
> @MAKEFLAGS="-j1 ${MAKEFLAGS}" ${MAKE} -f makefile hello
> hello:
> @echo Hello
Sorry for the delay. I wanted to say that, in addition to not doing
what you intended (changing the number of parallel jobs in a recursive
make), which I discussed last week, the above is actually wrong
(including in older versions of GNU make).
It will work, UNLESS you provide certain options. I think that's what
Dmitry was getting at with the --print-options thing but it might be
easier to see with a different flag, like "-s" (silent mode).
It has always been true (not changed in 4.x) that the MAKEFLAGS
variable has a first word which is either empty, or contains the
single-letter options with no arguments, AND NO PRECEDING "-".
So if you run "make" then MAKEFLAGS has an empty value. If you run
"make --no-print-directory" then MAKEFLAGS has the value
" --no-print-directory" (note very carefully the leading space here!)
If you run "make -s" then MAKEFLAGS has the value "s" (note, no leading
space AND no leading "-"!)
In your makefile above, if you run "make -s" then the sub-make is
invoked with MAKEFLAGS="-j1 s". That "s" is not treated as an option:
it's ignored (probably make should warn about this) so now you've lost
your "silent" option. You can see this with your makefile above, and
ANY version of GNU make, by removing the "@" from the echo line and
running it like this:
$ make
MAKEFLAGS="-j1 " make -f makefile hello
make[1]: Entering directory '/tmp'
echo Hello
Hello
make[1]: Leaving directory '/tmp'
Note how we make prints the recipe "echo hello". Now if we ran
"make -s" instead we would expect to see that line NOT printed because
we run in silent mode; here's what we get:
$ make -s
make[1]: Entering directory '/tmp'
echo Hello
Hello
make[1]: Leaving directory '/tmp'
Note here, the top-level makefile is silent because the "-s" option was
in effect, BUT the sub-make was not silent: we lost the "-s" option as
I described above.
Andreas is correct, if you want to add options to MAKEFLAGS you MUST
add the "-". Luckily, make ignores a single "-" in MAKEFLAGS so you
don't have to get more complicated:
all:
@MAKEFLAGS="-j1 -${MAKEFLAGS}" ${MAKE} -f makefile hello
I believe this works in all versions of GNU make.
But as I said in my previous email, you can't change the value of N in
-jN using this method (or any other method).
