Print control sequences instead of executing /bin/clear

Change of strategy allows users to specify '-c' twice to erase the
scrollback buffer.

NEWS

@@ -1,6 +1,8 @@
 = Next Release: 4.8
 
  - Set a maximum of 2^19 watches to guard against absurd file open limits
+ - Use control sequences to clear the display and specify '-c' twice to erase
+   the scrollback buffer
 
 = Release History
 

entr.1

@@ -13,7 +13,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd January 02, 2021
+.Dd February 18, 2021
 .Dt ENTR 1
 .Os
 .Sh NAME
@@ -47,11 +47,10 @@ This option has no effect in conjunction with the
 .Fl r
 flag.
 .It Fl c
-Execute
-.Pa /usr/bin/clear
-before invoking the
+Clear the screen before invoking the
 .Ar utility
 specified on the command line.
+Specify twice to erase the scrollback buffer.
 .It Fl d
 Track the directories of regular files provided as input and exit if a new file
 is added.

entr.c

@@ -372,7 +372,7 @@ set_options(char *argv[]) {
 			aggressive_opt = 1;
 			break;
 		case 'c':
-			clear_opt = 1;
+			clear_opt = clear_opt ? 2 : 1;
 			break;
 		case 'd':
 			dirwatch_opt = 1;
@@ -461,8 +461,16 @@ run_utility(char *argv[]) {
 		err(1, "can't fork");
 
 	if (pid == 0) {
+		/* 2J - erase the entire display
+		 * 3J - clear scrollback buffer
+		 * H  - set cursor position to the default
+		 */
 		if (clear_opt == 1)
-			system("/usr/bin/clear");
+			printf("\033[2J\033[H");
+		if (clear_opt == 2)
+			printf("\033[2J\033[3J\033[H");
+		fflush(stdout);
+
 		/* Set process group so subprocess can be signaled */
 		if (restart_opt == 1) {
 			setpgid(0, getpid());

entr_spec.c

@@ -797,6 +797,19 @@ int set_options_07() {
 	return 0;
 }
 
+/*
+ * Parse command line arguments with the clear scrollback option
+ */
+int set_options_08() {
+	int argv_offset;
+	char *argv[] = { "entr", "-cc", "echo", NULL };
+
+	argv_offset = set_options(argv);
+
+	ok(clear_opt == 2);
+	return 0;
+}
+
 /*
  * In restart mode the first action should be to start the server
  */
@@ -957,6 +970,7 @@ int test_main(int argc, char *argv[]) {
 	run(set_options_05);
 	run(set_options_06);
 	run(set_options_07);
+	run(set_options_08);
 	run(watch_fd_restart_01);
 	run(watch_fd_restart_02);
 	run(run_utility_01);