just want to make sure i understand the details of exporting
variables in gnu make.
first, if i set an environment variable either in the shell with:
$ VAR=value
$ export VAR
$ make ...
or as a one-time thing on the make command line with:
$ VAR=value make ...
is it true that that variable VAR is now part of the make invocation
environment and through all sub-make invocations? that is, there is no
need for me to "export" that variable agin in my Makefile -- it
wouldn't hurt but it's superfluous, and those two ways of doing it are
entirely equivalent? am i right so far?
also, if i do the above, in any part of that invocation, i can
reassign the value of VAR, that new value would now be part of the
environment at that level and all further sub-makes, and there is of
course no need to "export" that variable again -- once it's part of
the environment, it stays in the environment (short of explicitly
"unexport"ing it). still good so far?
next, i can always explicitly add a variable to the environment
within a Makefile with:
export VAR
but if that variable is *already* in my environment from the command
line, the make "export" directive is superfluous -- again, doesn't
hurt, just unnecessary.
finally, if i change the origin of the variable to:
$ make VAR=value ...
is that variable still part of the environment? i realize that i have
the freedom to check the origin of a variable from within a Makefile,
but how does that last construct work with the environment compared to
the first versions? thanks muchly.
rday
--
========================================================================
Robert P. J. Day Ottawa, Ontario, CANADA
http://crashcourse.ca
Twitter: http://twitter.com/rpjday
LinkedIn: http://ca.linkedin.com/in/rpjday
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