Also note that, if the --install option is used, any .m4file containing a required macro that is found in a directory listed inACLOCAL_PATH will be installed locally.In this case, serial numbers in .m4 are honored too,see Serial Numbers.
One reason why you should keep --install in the flags evenafter the first run is that when you later edit configure.acand depend on a new macro, this macro will be installed in yourm4/ automatically. Another one is that serial numbers(see Serial Numbers) can be used to update the macros in your source treeautomatically when new system-wide versions are installed. A serialnumber should be a single line of the form
driver toolkit 8.3.3 serial number
where nnn contains only digits and dots. It should appear inthe M4 file before any macro definition. It is a good practice tomaintain a serial number for each macro you distribute, even if you donot use the --install option of aclocal: this allowsother people to use it.
When aclocal sees a greater serial number, it immediatelyforgets anything it knows from files that have the same basename and asmaller serial number. So after it has found/usr/share/aclocal/thirdparty.m4 with serial 2,aclocal will proceed as if it had never seenm4/thirdparty.m4. This brings us back to a situation similarto that at the beginning of our example, where no local file definedthe macro. aclocal will install the new version of themacro in m4/thirdparty.m4, in this case overriding the oldversion. MyPackage just had its macro updated as a side effect ofrunning aclocal. 2ff7e9595c