include directive tells
make to suspend reading the
current makefile and read one or more other makefiles before continuing.
The directive is a line in the makefile that looks like this:
filenames can contain shell file name patterns. If
filenames is empty, nothing is included and no error is printed.
Extra spaces are allowed and ignored at the beginning of the line, but
a tab is not allowed. (If the line begins with a tab, it will be
considered a command line.) Whitespace is required between
include and the file names, and between file names; extra
whitespace is ignored there and at the end of the directive. A
comment starting with ‘#’ is allowed at the end of the line. If
the file names contain any variable or function references, they are
expanded. See How to Use Variables.
For example, if you have three .mk files, a.mk,
b.mk, and c.mk, and
$(bar) expands to
bish bash, then the following expression
include foo *.mk $(bar)
is equivalent to
include foo a.mk b.mk c.mk bish bash
make processes an
include directive, it suspends
reading of the containing makefile and reads from each listed file in
turn. When that is finished,
make resumes reading the
makefile in which the directive appears.
One occasion for using
include directives is when several programs,
handled by individual makefiles in various directories, need to use a
common set of variable definitions
(see Setting Variables) or pattern rules
(see Defining and Redefining Pattern Rules).
Another such occasion is when you want to generate prerequisites from
source files automatically; the prerequisites can be put in a file that
is included by the main makefile. This practice is generally cleaner
than that of somehow appending the prerequisites to the end of the main
makefile as has been traditionally done with other versions of
make. See Automatic Prerequisites.
If the specified name does not start with a slash, and the file is not
found in the current directory, several other directories are searched.
First, any directories you have specified with the ‘-I’ or
‘--include-dir’ option are searched
(see Summary of Options).
Then the following directories (if they exist)
are searched, in this order:
prefix/include (normally /usr/local/include
If an included makefile cannot be found in any of these directories, a
warning message is generated, but it is not an immediately fatal error;
processing of the makefile containing the
Once it has finished reading makefiles,
make will try to remake
any that are out of date or don't exist.
See How Makefiles Are Remade.
Only after it has tried to find a way to remake a makefile and failed,
make diagnose the missing makefile as a fatal error.
If you want
make to simply ignore a makefile which does not exist
and cannot be remade, with no error message, use the
directive instead of
include, like this:
This acts like
include in every way except that there is no
error (not even a warning) if any of the filenames do not exist.
For compatibility with some other
sinclude is another name for
 GNU Make compiled for MS-DOS and MS-Windows behaves as if prefix has been defined to be the root of the DJGPP tree hierarchy.