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make
Flags such as `-s' and `-k' are passed automatically to the
sub-make through the variable MAKEFLAGS. This variable is
set up automatically by make to contain the flag letters that
make received. Thus, if you do `make -ks' then
MAKEFLAGS gets the value `ks'.
As a consequence, every sub-make gets a value for MAKEFLAGS
in its environment. In response, it takes the flags from that value and
processes them as if they had been given as arguments.
See section Summary of Options.
The options `-C', `-f', `-I', `-o', and `-W'
are not put into MAKEFLAGS; these options are not passed down.
The `-j' option is a special case (see section Parallel Execution).
If you set it to some numeric value, `-j 1' is always put into
MAKEFLAGS instead of the value you specified. This is because if
the `-j' option were passed down to sub-makes, you would
get many more jobs running in parallel than you asked for. If you give
`-j' with no numeric argument, meaning to run as many jobs as
possible in parallel, this is passed down, since multiple infinities are
no more than one.
If you do not want to pass the other flags down, you must change the
value of MAKEFLAGS, like this:
MAKEFLAGS=
subsystem:
cd subdir; $(MAKE)
or like this:
subsystem:
cd subdir; $(MAKE) MAKEFLAGS=
A similar variable MFLAGS exists also, for historical compatibility.
It has the same value as MAKEFLAGS except that it always begins with
a hyphen unless it is empty (MAKEFLAGS begins with a hyphen only when
it begins with an option that has no single-letter version, such as
`--warn-undefined-variables'). MFLAGS was traditionally used
explicitly in the recursive make command, like this:
subsystem:
cd subdir; $(MAKE) $(MFLAGS)
but now MAKEFLAGS makes this usage redundant. If you want your
makefiles to be compatible with old make programs, use this
technique; it will work fine with more modern make versions too.
The MAKEFLAGS variable can also be useful if you want to have
certain options, such as `-k' (see section Summary of Options), set each time you run make. You simply put a value for
MAKEFLAGS in your environment. You can also set MAKEFLAGS in
a makefile, to specify additional flags that should also be in effect for
that makefile. (Note that you cannot use MFLAGS this way. That
variable is set only for compatibility; make does not interpret a
value you set for it in any way.)
When make interprets the value of MAKEFLAGS (either from the
environment or from a makefile), it first prepends a hyphen if the value
does not already begin with one. Then it chops the value into words
separated by blanks, and parses these words as if they were options given
on the command line (except that `-C', `-f', `-h',
`-o', `-W', and their long-named versions are ignored; and there
is no error for an invalid option).
If you do put MAKEFLAGS in your environment, you should be sure not
to include any options that will drastically affect the actions of
make and undermine the purpose of makefiles and of make
itself. For instance, the `-t', `-n', and `-q' options, if
put in one of these variables, could have disastrous consequences and would
certainly have at least surprising and probably annoying effects.
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