eizoctl: add an option to filter by serial number

It turns out that this is actually critical when switching inputs
in certain wild setups.

README.adoc

@@ -70,6 +70,17 @@ exe := A_Startup . "\eizoctltray.exe"
 }
 ```
 
+On macOS, the simplest way to bind keyboard shortcuts is the Shortcuts app,
+with _Run Shell Scripts_ actions:
+
+```
+/Applications/eizoctltray.app/Contents/MacOS/eizoctltray -q --input HDMI
+```
+
+If you have issues with entering a specific key combination, like I did
+with ^⌘F1 etc., try changing it later within _System Settings_ → _Keyboard_ →
+_Keyboard Shortcuts..._ → _Services_ → _Shortcuts_.
+
 elksmart-comm
 ~~~~~~~~~~~~~
 _elksmart-comm_ interfaces with ELK Smart infrared dongles EKX4S and EKX5S-T,

eizoctl.c

@@ -1037,6 +1037,10 @@ eizo_watch(struct eizo_monitor *m, print_fn output, print_fn error)
 }
 
 static const char *usage = "Usage: %s OPTION...\n\n"
+	"  -l, --list\n"
+	"   List all connected EIZO monitors, with their serial number.\n"
+	"  -s, --serial SERIAL\n"
+	"   Only act on the monitor matching the specified serial number.\n"
 	"  -b, --brightness [+-]BRIGHTNESS\n"
 	"   Change monitor brightness; values go from 0 to 1 and may be relative.\n"
 	"  -i, --input NAME\n"
@@ -1057,6 +1061,8 @@ run(int argc, char *argv[], print_fn output, print_fn error)
 {
 	const char *name = argv[0];
 	static struct option opts[] = {
+		{"list", no_argument, NULL, 'l'},
+		{"serial", required_argument, NULL, 's'},
 		{"brightness", required_argument, NULL, 'b'},
 		{"input", required_argument, NULL, 'i'},
 		{"restart", no_argument, NULL, 'r'},
@@ -1069,11 +1075,17 @@ run(int argc, char *argv[], print_fn output, print_fn error)
 
 	int quiet = 0;
 	double brightness = NAN;
-	bool relative = false, restart = false, events = false;
+	bool list = false, relative = false, restart = false, events = false;
-	const char *port = NULL;
+	const char *serial = NULL, *port = NULL;
 	int c = 0;
-	while ((c = getopt_long(argc, argv, "b:i:reqhV", opts, NULL)) != -1)
+	while ((c = getopt_long(argc, argv, "ls:b:i:reqhV", opts, NULL)) != -1)
 		switch (c) {
+		case 'l':
+			list = true;
+			break;
+		case 's':
+			serial = optarg;
+			break;
 		case 'b':
 			relative = *optarg == '+' || *optarg == '-';
 			if (sscanf(optarg, "%lf", &brightness) && isfinite(brightness))
@@ -1123,8 +1135,6 @@ run(int argc, char *argv[], print_fn output, print_fn error)
 	if (quiet > 1)
 		error = print_dummy;
 
-	// It should be possible to choose a particular monitor,
-	// but it is generally more useful to operate on all of them.
 	struct hid_device_info *devs = hid_enumerate(USB_VID_EIZO, 0), *p = devs;
 	for (; p; p = p->next) {
 		struct eizo_monitor m = {};
@@ -1133,6 +1143,15 @@ run(int argc, char *argv[], print_fn output, print_fn error)
 			continue;
 		}
 
+		if (list)
+			output("%s %s\n", m.product, m.serial);
+
+		// Generously assuming that different products/models
+		// don't share serial numbers,
+		// which would otherwise deserve another filtering option.
+		if (serial && strcmp(serial, m.serial))
+			goto next;
+
 		if (isfinite(brightness)) {
 			double prev = 0.;
 			if (!eizo_get_brightness(&m, &prev)) {
@@ -1177,6 +1196,7 @@ run(int argc, char *argv[], print_fn output, print_fn error)
 				error("%s\n", m.error);
 		}
 
+	next:
 		eizo_monitor_close(&m);
 	}
 	hid_free_enumeration(devs);