commit https://github.com/vim/vim/commit/2cab0e191055a8145ccd46cd52869fbb9798b971 Author: Bram Moolenaar <Bram@vim.org> Date: Thu Nov 24 15:09:07 2016 +0100 patch 8.0.0096 Problem: When the input or output is not a tty Vim appears to hang. Solution: Add the --ttyfail argument. Also add the "ttyin" and "ttyout" features to be able to check in Vim script.

--- a/src/structs.h
+++ b/src/structs.h
@@ -3225,8 +3225,8 @@ typedef struct
 #endif
 
     int		want_full_screen;
-    int		stdout_isatty;		/* is stdout a terminal? */
     int		not_a_term;		/* no warning for missing term? */
+    int		tty_fail;		/* exit if not a tty */
     char_u	*term;			/* specified terminal name */
 #ifdef FEAT_CRYPT
     int		ask_for_key;		/* -x argument */