Shell: Add a 'kill' builtin that wraps the system's own

Fixes #6578.

Userland/Shell/Builtin.cpp

@@ -1031,6 +1031,43 @@ int Shell::builtin_not(int argc, const char** argv)
     return exit_code == 0 ? 1 : 0;
 }
 
+int Shell::builtin_kill(int argc, const char** argv)
+{
+    // Simply translate the arguments and pass them to `kill'
+    Vector<String> replaced_values;
+    auto kill_path = find_in_path("kill");
+    if (kill_path.is_empty()) {
+        warnln("kill: `kill' not found in PATH");
+        return 126;
+    }
+    replaced_values.append(kill_path);
+    for (auto i = 1; i < argc; ++i) {
+        if (auto job_id = resolve_job_spec(argv[i]); job_id.has_value()) {
+            auto job = find_job(job_id.value());
+            if (job) {
+                replaced_values.append(String::number(job->pid()));
+            } else {
+                warnln("kill: Job with pid {} not found", job_id.value());
+                return 1;
+            }
+        } else {
+            replaced_values.append(argv[i]);
+        }
+    }
+
+    // Now just run `kill'
+    AST::Command command;
+    command.argv = move(replaced_values);
+    command.position = m_source_position.has_value() ? m_source_position->position : Optional<AST::Position> {};
+
+    auto exit_code = 1;
+    if (auto job = run_command(command)) {
+        block_on_job(job);
+        exit_code = job->exit_code();
+    }
+    return exit_code;
+}
+
 bool Shell::run_builtin(const AST::Command& command, const NonnullRefPtrVector<AST::Rewiring>& rewirings, int& retval)
 {
     if (command.argv.is_empty())

Userland/Shell/Shell.cpp

@@ -1194,6 +1194,27 @@ String Shell::unescape_token(const String& token)
     return builder.build();
 }
 
+String Shell::find_in_path(const StringView& program_name)
+{
+    String path = getenv("PATH");
+    if (!path.is_empty()) {
+        auto directories = path.split(':');
+        for (const auto& directory : directories) {
+            Core::DirIterator programs(directory.characters(), Core::DirIterator::SkipDots);
+            while (programs.has_next()) {
+                auto program = programs.next_path();
+                auto program_path = String::formatted("{}/{}", directory, program);
+                if (access(program_path.characters(), X_OK) != 0)
+                    continue;
+                if (program == program_name)
+                    return program_path;
+            }
+        }
+    }
+
+    return {};
+}
+
 void Shell::cache_path()
 {
     if (!m_is_interactive)

Userland/Shell/Shell.h

@@ -46,7 +46,8 @@
     __ENUMERATE_SHELL_BUILTIN(fg)      \
     __ENUMERATE_SHELL_BUILTIN(bg)      \
     __ENUMERATE_SHELL_BUILTIN(wait)    \
-    __ENUMERATE_SHELL_BUILTIN(dump)
+    __ENUMERATE_SHELL_BUILTIN(dump)    \
+    __ENUMERATE_SHELL_BUILTIN(kill)
 
 #define ENUMERATE_SHELL_OPTIONS()                                                                                    \
     __ENUMERATE_SHELL_OPTION(inline_exec_keep_empty_segments, false, "Keep empty segments in inline execute $(...)") \
@@ -103,6 +104,8 @@ public:
     String resolve_path(String) const;
     String resolve_alias(const String&) const;
 
+    static String find_in_path(const StringView& program_name);
+
     static bool has_history_event(StringView);
 
     RefPtr<AST::Value> get_argument(size_t);