Remove -n for ignoring system headers. Instead add finer grain shell

macros and document them.

Prompted by:	bde

1 files changed, 20 insertions, 3 deletions

diff --git a/usr.bin/mkdep/mkdep.1 b/usr.bin/mkdep/mkdep.1
index 2add91dc4103..8116f47907f8 100644
--- a/usr.bin/mkdep/mkdep.1
+++ b/usr.bin/mkdep/mkdep.1
@@ -39,7 +39,7 @@
 .Nd construct Makefile dependency list
 .Sh SYNOPSIS
 .Nm
-.Op Fl anp
+.Op Fl ap
 .Op Fl f Ar file
 .Op Ar flags
 .Ar file ...
@@ -60,6 +60,15 @@ depend:
 where the macro SRCS is the list of C source files and the macro
 CFLAGS is the list of flags for the C compiler.
 .Pp
+The user has the ability to change the preprocessor and preprocessor options
+used.  For instance, to use Gcc as the preprocessor and to ignore system
+headers, one would use
+.Bd -literal -offset indent
+depend:
+	env MKDEP_CPP="gcc -E" MKDEP_CPP_OPTS=-MM mkdep \\
+		${CFLAGS} ${SRCS}
+.Ed
+.Pp
 The options are as follows:
 .Bl -tag -width Ds
 .It Fl a
@@ -71,8 +80,6 @@ may be run from a single Makefile.
 Write the include file dependencies to 
 .Ar file ,
 instead of the default ``.depend''.
-.It Fl n
-Don't make dependencies on system headers.  I.e. anything in <>'s.
 .It Fl p
 Cause
 .Nm
@@ -88,6 +95,16 @@ directly from its C module rather than using an intermediate
 module.
 This is useful for programs whose source is contained in a single
 module.
+.Sh ENVIRONMENT
+.Bl -tag -width MKDEP_CPP_OPTS
+.It Ev CC
+Specifies the C compiler to use.  The specified compiler is expected to have
+options consistant with the Gnu C compiler.
+.It Ev MKDEP_CPP
+Specifies the preprocessor to use.  The default is "${CC} -E".
+.It Ev MKDEP_CPP_OPTS
+Specifie the non-CFLAGS options for the preprocessor.  The default is
+"-M".
 .El
 .Sh SEE ALSO
 .Xr cc 1 ,