use macro for /usr/local/plan9
diff --git a/man/man1/rm.1 b/man/man1/rm.1
index a2ab0d1..83bc817 100644
--- a/man/man1/rm.1
+++ b/man/man1/rm.1
@@ -23,6 +23,6 @@
 entire contents of a directory
 and the directory itself.
 .SH SOURCE
-.B /usr/local/plan9/src/cmd/rm.c
+.B \*9/src/cmd/rm.c
 .SH "SEE ALSO"
 .IR remove (3)