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/globals.h
+++ b/src/globals.h
@@ -643,6 +643,8 @@ EXTERN int	exiting INIT(= FALSE);
 EXTERN int	really_exiting INIT(= FALSE);
 				/* TRUE when we are sure to exit, e.g., after
 				 * a deadly signal */
+EXTERN int	stdout_isatty INIT(= TRUE);	/* is stdout a terminal? */
+
 #if defined(FEAT_AUTOCHDIR)
 EXTERN int	test_autochdir INIT(= FALSE);
 #endif