autoconf: Special Chars in Names

1 
1 12.3 Special Characters in Make Macro Names
1 ===========================================
1 
1 Posix limits macro names to nonempty strings containing only ASCII
1 letters and digits, `.', and `_'.  Many `make' implementations allow a
1 wider variety of characters, but portable makefiles should avoid them.
1 It is portable to start a name with a special character, e.g.,
1 `$(.FOO)'.
1 
1    Some ancient `make' implementations don't support leading
1 underscores in macro names.  An example is NEWS-OS 4.2R.
1 
1      $ cat Makefile
1      _am_include = #
1      _am_quote =
1      all:; @echo this is test
1      $ make
1      Make: Must be a separator on rules line 2.  Stop.
1      $ cat Makefile2
1      am_include = #
1      am_quote =
1      all:; @echo this is test
1      $ make -f Makefile2
1      this is test
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1 However, this problem is no longer of practical concern.
1