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General Conventions for Makefiles

Every Makefile should contain this line:

SHELL = /bin/sh

to avoid trouble on systems where the SHELL variable might be inherited from the environment. (This is never a problem with GNU make.)

Different make programs have incompatible suffix lists and implicit rules, and this sometimes creates confusion or misbehavior. So it is a good idea to set the suffix list explicitly using only the suffixes you need in the particular Makefile, like this:

.SUFFIXES: .c .o

The first line clears out the suffix list, the second introduces all suffixes which may be subject to implicit rules in this Makefile.

Don't assume that `.' is in the path for command execution. When you need to run programs that are a part of your package during the make, please make sure that it uses `./' if the program is built as part of the make or `$(srcdir)/' if the file is an unchanging part of the source code. Without one of these prefixes, the current search path is used.

The distinction between `./' and `$(srcdir)/' is important when using the `--srcdir' option to `configure'. A rule of the form:

foo.1 : foo.man sedscript
        sed -e sedscript foo.man > foo.1

will fail when the current directory is not the source directory, because `foo.man' and `sedscript' are not in the current directory.

When using GNU make, relying on `VPATH' to find the source file will work in the case where there is a single dependency file, since the make automatic variable `$<' will represent the source file wherever it is. (Many versions of make set `$<' only in implicit rules.) A Makefile target like

foo.o : bar.c
        $(CC) -I. -I$(srcdir) $(CFLAGS) -c bar.c -o foo.o

should instead be written as

foo.o : bar.c
        $(CC) -I. -I$(srcdir) $(CFLAGS) -c $< -o $@

in order to allow `VPATH' to work correctly. When the target has multiple dependencies, using an explicit `$(srcdir)' is the easiest way to make the rule work well. For example, the target above for `foo.1' is best written as:

foo.1 : foo.man sedscript
        sed -e $(srcdir)/sedscript $(srcdir)/foo.man > $@

Try to make the build and installation targets, at least (and all their subtargets) work correctly with a parallel make.

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