Allow selection of the affected terminal using redirection

of standard input or standard output, like mesg(1) does.

Suggested by:	sheldonh

2 files changed, 10 insertions, 1 deletions

diff --git a/usr.bin/biff/biff.1 b/usr.bin/biff/biff.1
index 49d711d..4a5ca9c 100644
--- a/usr.bin/biff/biff.1
+++ b/usr.bin/biff/biff.1
@@ -47,6 +47,13 @@ The
 utility informs the system whether you want to be notified when mail arrives
 during the current terminal session.
 .Pp
+Affected is the first terminal associated with the standard input,
+standard output or standard error file descriptor, in that order.
+Thus, it is possible to use the redirection facilities of a shell to
+toggle the notification for other terminals than the one
+.Nm
+runs on.
+.Pp
 The following options are available:
 .Bl -tag -width indent
 .It Cm n
diff --git a/usr.bin/biff/biff.c b/usr.bin/biff/biff.c
index 938914c..acfd10b 100644
--- a/usr.bin/biff/biff.c
+++ b/usr.bin/biff/biff.c
@@ -74,7 +74,9 @@ main(argc, argv)
 	argc -= optind;
 	argv += optind;
 
-	if ((name = ttyname(STDERR_FILENO)) == NULL)
+	if ((name = ttyname(STDIN_FILENO)) == NULL &&
+	    (name = ttyname(STDOUT_FILENO)) == NULL &&
+	    (name = ttyname(STDERR_FILENO)) == NULL)
 		err(2, "unknown tty");
 
 	if (stat(name, &sb))