use macro for /usr/local/plan9
diff --git a/man/man1/sort.1 b/man/man1/sort.1
index 4400f0a..eb0d7f4 100644
--- a/man/man1/sort.1
+++ b/man/man1/sort.1
@@ -238,7 +238,7 @@
 .SH FILES
 .BI /tmp/sort. <pid>.<ordinal>
 .SH SOURCE
-.B /usr/local/plan9/src/cmd/sort.c
+.B \*9/src/cmd/sort.c
 .SH SEE ALSO
 .IR uniq (1),
 .IR look (1)