(m4.info) Include

 
 Including named files
 =====================
 
    There are two builtin macros in `m4' for including files:
 
      include(FILENAME)
      sinclude(FILENAME)
 
 both of which cause the file named FILENAME to be read by `m4'.  When
 the end of the file is reached, input is resumed from the previous
 input file.
 
    The expansion of `include' and `sinclude' is therefore the contents
 of FILENAME.
 
    It is an error for an `include'd file not to exist.  If you do not
 want error messages about non-existent files, `sinclude' can be used to
 include a file, if it exists, expanding to nothing if it does not.
 
      include(`no-such-file')
      =>
      error-->30.include:2: m4: Cannot open no-such-file: No such file or directory
      sinclude(`no-such-file')
      =>
 
    Assume in the following that the file `incl.m4' contains the lines:
      Include file start
      foo
      Include file end
 
 Normally file inclusion is used to insert the contents of a file into
 the input stream.  The contents of the file will be read by `m4' and
 macro calls in the file will be expanded:
 
      define(`foo', `FOO')
      =>
      include(`incl.m4')
      =>Include file start
      =>FOO
      =>Include file end
      =>
 
    The fact that `include' and `sinclude' expand to the contents of the
 file can be used to define macros that operate on entire files.  Here
 is an example, which defines `bar' to expand to the contents of
 `incl.m4':
 
      define(`bar', include(`incl.m4'))
      =>
      This is `bar':  >>>bar<<<
      =>This is bar:  >>>Include file start
      =>foo
      =>Include file end
      =><<<
 
    This use of `include' is not trivial, though, as files can contain
 quotes, commas and parentheses, which can interfere with the way the
 `m4' parser works.
 
    The builtin macros `include' and `sinclude' are recognized only when
 given arguments.
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