use macro for /usr/local/plan9
diff --git a/man/man3/sendfd.3 b/man/man3/sendfd.3
index 8090dfc..771bd9a 100644
--- a/man/man3/sendfd.3
+++ b/man/man3/sendfd.3
@@ -49,7 +49,7 @@
 between processes, but the kernel structure it represents
 will not.
 .SH SOURCE
-.B /usr/local/plan9/src/lib9/sendfd.c
+.B \*9/src/lib9/sendfd.c
 .SH SEE ALSO
 .IR socketpair (2),
 .I sendmsg