userspace: Implement `dirname` utility

userspace/programs/CMakeLists.txt

@@ -7,6 +7,7 @@ set(USERSPACE_PROGRAMS
 	cp
 	dd
 	dhcp-client
+	dirname
 	DynamicLoader
 	echo
 	env

userspace/programs/dirname/CMakeLists.txt

@@ -0,0 +1,8 @@
+set(SOURCES
+	main.cpp
+)
+
+add_executable(dirname ${SOURCES})
+banan_link_library(dirname libc)
+
+install(TARGETS dirname OPTIONAL)

userspace/programs/dirname/main.cpp

@@ -0,0 +1,18 @@
+#include <libgen.h>
+#include <stdio.h>
+
+int usage(const char* argv0, int ret)
+{
+	FILE* fout = ret ? stderr : stdout;
+	fprintf(fout, "usage: %s STRING\n", argv0);
+	return ret;
+}
+
+int main(int argc, const char* argv[])
+{
+	if (argc != 2)
+		return usage(argv[0], 1);
+	const char* result = dirname(const_cast<char*>(argv[1]));
+	printf("%s\n", result);
+	return 0;
+}