dirname: Support options and multiple strings

This is not needed by POSIX but sdl2-config uses `dirname -- "$0"`

userspace/programs/dirname/main.cpp

@@ -1,18 +1,56 @@
+#include <getopt.h>
 #include <libgen.h>
 #include <stdio.h>
 
-int usage(const char* argv0, int ret)
+int main(int argc, char* argv[])
 {
-	FILE* fout = ret ? stderr : stdout;
-	fprintf(fout, "usage: %s STRING\n", argv0);
-	return ret;
+	bool zero = false;
+
+	for (;;)
+	{
+		static option long_options[] {
+			{ "zero", no_argument, nullptr, 'z' },
+			{ "help", no_argument, nullptr, 'h' },
+		};
+
+		int ch = getopt_long(argc, argv, "zh", long_options, nullptr);
+		if (ch == -1)
+			break;
+
+		switch (ch)
+		{
+			case 'z':
+				zero = true;
+				break;
+			case 'h':
+				fprintf(stderr, "usage: %s [OPTIONS]...\n", argv[0]);
+				fprintf(stderr, "  control the audio server\n");
+				fprintf(stderr, "OPTIONS:\n");
+				fprintf(stderr, "  -l, --list      list devices and their pins\n");
+				fprintf(stderr, "  -d, --device N  set device index N as the current one\n");
+				fprintf(stderr, "  -p, --pin N     set pin N as the current one\n");
+				fprintf(stderr, "  -v, --volume N  set volume to N%%. if + or - is given, volume is relative to the current volume\n");
+				fprintf(stderr, "  -h, --help      show this message and exit\n");
+				return 0;
+			case '?':
+				fprintf(stderr, "invalid option %c\n", optopt);
+				fprintf(stderr, "see '%s --help' for usage\n", argv[0]);
+				return 1;
+		}
 	}
 
-int main(int argc, const char* argv[])
+	if (optind >= argc)
 	{
-	if (argc != 2)
-		return usage(argv[0], 1);
-	const char* result = dirname(const_cast<char*>(argv[1]));
-	printf("%s\n", result);
+		fprintf(stderr, "missing operand\n");
+		fprintf(stderr, "see '%s --help' for usage\n", argv[0]);
+		return 1;
+	}
+
+	for (int i = optind; i < argc; i++)
+	{
+		printf("%s", dirname(argv[i]));
+		putchar(zero ? '\0' : '\n');
+	}
+
 	return 0;
 }