Re: On double colon(::) use

[Paul D. Smith]

%% kaiduan xie <address@hidden> writes:

  kx> I felt a littel difficulty to understand the use of double colon(::),

Basically, a double-colon rule allows you to supply multiple separate
command scripts.  For example, if you do this:

  foo:
        do some commands
  foo:
        do some other commands

then make will complain because you've defined two different sets of
commands to run to build one target "foo".  GNU make will complain, then
ignore the earlier set of commands and use only the latest set.

But if you use double-colon rules:

  foo::
        do some commands
  foo::
        do some other commands

Now make will not complain, and if it wants to rebuild foo it will run
_BOTH_ sets of commands.

There are some other details which you can discover in the GNU make
manual.

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