use macro for /usr/local/plan9
diff --git a/man/man3/pipe.3 b/man/man3/pipe.3
index 993e33a..10decb6 100644
--- a/man/man3/pipe.3
+++ b/man/man3/pipe.3
@@ -57,7 +57,7 @@
 will return 0 bytes.  Writes to a pipe with no reader will generate a note
 .BR "sys: write on closed pipe" .
 .SH SOURCE
-.B /usr/local/plan9/src/lib9/pipe.c
+.B \*9/src/lib9/pipe.c
 .SH SEE ALSO
 .IR intro (3),
 .IR read (3)