apps: Add time

apps/CMakeLists.txt

@@ -27,3 +27,4 @@ luna_app(ipc-test.cpp ipc-test)
 luna_app(mount.cpp mount)
 luna_app(umount.cpp umount)
 luna_app(ps.cpp ps)
+luna_app(time.cpp time)

apps/time.cpp

@@ -0,0 +1,45 @@
+#include <os/ArgumentParser.h>
+#include <os/File.h>
+#include <os/Process.h>
+#include <stdio.h>
+#include <sys/resource.h>
+#include <sys/wait.h>
+
+Result<int> luna_main(int argc, char** argv)
+{
+    Vector<StringView> command;
+
+    os::ArgumentParser parser;
+    parser.add_description("Time a command.");
+    parser.add_system_program_info("time"_sv);
+    parser.set_vector_argument(command, true);
+    TRY(parser.parse(argc, argv));
+
+    auto pid = TRY(os::Process::fork());
+
+    if (pid == 0)
+    {
+        TRY(os::Process::exec(command[0], command.slice()));
+        unreachable();
+    }
+
+    if (waitpid(pid, nullptr, 0) < 0)
+    {
+        perror("waitpid");
+        return 1;
+    }
+
+    struct rusage usage;
+    if (getrusage(RUSAGE_CHILDREN, &usage) < 0)
+    {
+        perror("getrusage");
+        return 1;
+    }
+
+    auto cmdline = TRY(String::join(command, " "));
+
+    os::println("%s  %d.%.2ds user %d.%.2ds system"_sv, cmdline.chars(), usage.ru_utime.tv_sec,
+                usage.ru_utime.tv_usec / 10000, usage.ru_stime.tv_sec, usage.ru_stime.tv_usec / 10000);
+
+    return 0;
+}