Fix some posixshmcontrol nits.

- Exit with an error if no path is specified.
- Man page typo.
- Error message typo.

Reviewed by:	kib
Sponsored by:	Juniper Networks, Inc.
Sponsored by:	Klara, Inc.
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D26376

usr.bin/posixshmcontrol/posixshmcontrol.1

@@ -120,7 +120,7 @@ using name-switch services, instead the raw numeric values are printed.
 To show content of the shared memory segment with the path
 .Pa /1 ,
 use the command
-.Dl "posixshmcontrol dump /q | hexdump -C"
+.Dl "posixshmcontrol dump /1 | hexdump -C"
 .It
 To create a segment with the path
 .Pa /2

usr.bin/posixshmcontrol/posixshmcontrol.c

@@ -147,9 +147,14 @@ create_shm(int argc, char **argv)
 			return (2);
 		}
 	}
-
 	argc -= optind;
 	argv += optind;
+
+	if (argc == 0) {
+		usage();
+		return (2);
+	}
+
 	ret = 0;
 	for (i = 0; i < argc; i++) {
 		ret1 = create_one_shm(argv[i], mode, idx);
@@ -179,6 +184,11 @@ delete_shm(int argc, char **argv)
 {
 	int i, ret, ret1;
 
+	if (argc == 1) {
+		usage();
+		return (2);
+	}
+
 	ret = 0;
 	for (i = 1; i < argc; i++) {
 		ret1 = delete_one_shm(argv[i]);
@@ -347,6 +357,11 @@ read_shm(int argc, char **argv)
 {
 	int i, ret, ret1;
 
+	if (argc == 1) {
+		usage();
+		return (2);
+	}
+
 	ret = 0;
 	for (i = 1; i < argc; i++) {
 		ret1 = read_one_shm(argv[i]);
@@ -433,6 +448,11 @@ stat_shm(int argc, char **argv)
 	argc -= optind;
 	argv += optind;
 
+	if (argc == 0) {
+		usage();
+		return (2);
+	}
+
 	ret = 0;
 	for (i = 0; i < argc; i++) {
 		ret1 = stat_one_shm(argv[i], hsize, uname);
@@ -473,16 +493,21 @@ truncate_shm(int argc, char **argv)
 		switch (c) {
 		case 's':
 			if (expand_number(optarg, &newsize) == -1)
-				err(1, "size:");
+				err(1, "size");
 			break;
 		case '?':
 		default:
 			return (2);
 		}
 	}
-
 	argc -= optind;
 	argv += optind;
+
+	if (argc == 0) {
+		usage();
+		return (2);
+	}
+
 	ret = 0;
 	for (i = 0; i < argc; i++) {
 		ret1 = truncate_one_shm(argv[i], newsize);