ncal(1) highlights the current date (or a date provided via parameter)

even if stdout is not a tty. If stdout is not a tty the data is
normally processed by other tools and no control sequences are
expected.

PR:		bin/158580
MFC after:	1 week

usr.bin/ncal/ncal.1

@@ -171,6 +171,8 @@ that, two after that and the whole year.
 will warn about these combinations.
 .Pp
 A year starts on January 1.
+.P
+Highlighting of dates is disabled if stdout is not a tty.
 .Sh SEE ALSO
 .Xr calendar 3 ,
 .Xr strftime 3

usr.bin/ncal/ncal.c

@@ -822,7 +822,8 @@ mkmonthr(int y, int m, int jd_flag, struct monthlines *mlines)
 					dt.d = j - jan1 + 1;
 				else
 					sdater(j, &dt);
-				if (j == highlightdate && !flag_nohighlight)
+				if (j == highlightdate && !flag_nohighlight
+				 && isatty(STDOUT_FILENO))
 					highlight(mlines->lines[i] + k,
 					    ds + dt.d * dw, dw, &l);
 				else