Re: make -U

From: Ruslan Ermilov (ru_at_FreeBSD.org)
Date: 08/02/03

  • Next message: Andrew Lankford: "Re: headsup: swap_pager.c" 
    Date: Sat, 2 Aug 2003 20:13:52 +0300
To: Faried Nawaz <fn@hungry.com>

    [ Moved to -arch ]

    > From the message in freebsd-hackers which first introduced
    > this patch:
    >
    > - Date: Tue, 29 Jul 2003 09:09:17 -0700
    > - From: Faried Nawaz <fn@hungry.com>
    > - Subject: patch to add make -U
    >
    > While working around a port issue (ports/55013), I discovered
    > that make couldn't unset variables using make -U. I've written
    > a small patch that adds -U functionality, but I haven't tested
    > it extensively.
    >
    > http://web.nilpotent.org/tmp/make.diff.bz2 (~ 3KB unpacked)
    > against yesterday's -CURRENT code.
    >
    The patch looks sane.

    > A simple Makefile I used to test it:
    >
    > -- cut here --
    > FOO = bar
    >
    > .ifdef FOO
    > SAY = y
    > .else
    > SAY = n
    > .endif
    >
    > all:
    > echo $(SAY)
    > -- cut here --
    >
    > Try "make -U FOO".
    >
    > Personally I think this is a reasonable option to implement.
    > An undefined variable is not the same as a variable which is
    > defined to be a null string.
    >
    I want that everyone understands the effect of the patch: the
    -U FOO option causes the FOO variable to always be reported
    by make(1) as undefined, not only in this makefile, but even
    in sub-make processes, and affects all makefiles wishing to
    set it -- it just doesn't let them do this, globally.

    So the actual meaning of this option is "prevent variable FOO
    from being set". (The implementation is somewhat different;
    it causes make(1) to lie that variable being is, but the net
    effect is the same.)

    Given the above, do we really want this option in our make?

    Cheers, 

    -- 
Ruslan Ermilov		Sysadmin and DBA,
ru@sunbay.com		Sunbay Software Ltd,
ru@FreeBSD.org		FreeBSD committer

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