Userspace: implement basic sleep command

userspace/CMakeLists.txt

@@ -19,6 +19,7 @@ set(USERSPACE_PROJECTS
 	poweroff
 	rm
 	Shell
+	sleep
 	snake
 	stat
 	sync

userspace/sleep/CMakeLists.txt

@@ -0,0 +1,16 @@
+cmake_minimum_required(VERSION 3.26)
+
+project(sleep CXX)
+
+set(SOURCES
+	main.cpp
+)
+
+add_executable(sleep ${SOURCES})
+target_compile_options(sleep PUBLIC -O2 -g)
+target_link_libraries(sleep PUBLIC libc)
+
+add_custom_target(sleep-install
+	COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_BINARY_DIR}/sleep ${BANAN_BIN}/
+	DEPENDS sleep
+)

userspace/sleep/main.cpp

@@ -0,0 +1,38 @@
+#include <ctype.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int usage(char* argv0, int ret)
+{
+	FILE* fp = (ret == 0) ? stdout : stderr;
+	fprintf(fp, "usage: %s SECONDS\n", argv0);
+	return ret;
+}
+
+int main(int argc, char** argv)
+{
+	if (argc != 2)
+		return usage(argv[0], 1);
+	
+	if (strlen(argv[1]) > 9)
+	{
+		fprintf(stderr, "SECONDS argument too large\n");
+		return usage(argv[0], 1);
+	}
+
+	int seconds = 0;
+	const char* ptr = argv[1];
+	while (*ptr)
+	{
+		if (!isdigit(*ptr))
+		{
+			fprintf(stderr, "invalid SECONDS argument\n");
+			return usage(argv[0], 1);
+		}
+		seconds = (seconds * 10) + (*ptr - '0');
+		ptr++;
+	}
+
+	sleep(seconds);
+}