команда по выводу значений System.properties

src/main/java/mc/server/Main.java

@@ -1,19 +1,48 @@
 package mc.server;
 
-import org.jline.reader.LineReader;
-import org.jline.reader.LineReaderBuilder;
-import org.jline.reader.UserInterruptException;
+import mc.server.shell.CommandStore;
+import org.jline.builtins.Builtins;
+import org.jline.builtins.CommandRegistry;
+import org.jline.reader.*;
+import org.jline.reader.impl.completer.NullCompleter;
+
+import java.io.PrintWriter;
+import java.util.Collections;
 
 public class Main {
 
     public static void main(String[] args) {
-        LineReader reader = LineReaderBuilder.builder().build();
+        CommandStore commandStore = new CommandStore();
+        commandStore.register("system-properties", new Builtins.CommandMethods(
+                commandInput -> {
+                    final PrintWriter writer = commandInput.terminal().writer();
+                    System.getProperties().forEach((key, value) ->
+                            writer.println(String.format("%s = %s", key, value.toString())));
+                },
+                commandName -> Collections.singletonList(NullCompleter.INSTANCE)
+        ));
+
+        final Completer completer = CommandRegistry.compileCompleters(commandStore);
+
+        final LineReader reader = LineReaderBuilder.builder()
+                .completer(completer)
+                .build();
 
         try {
+            final CommandRegistry.CommandSession session = new CommandRegistry.CommandSession(reader.getTerminal());
+            final PrintWriter terminalWriter = reader.getTerminal().writer();
             //noinspection InfiniteLoopStatement
             while (true) {
-                String line = reader.readLine();
-                System.out.println("line = '" + line + "'");
+                final String line = reader.readLine().trim();
+
+                final ParsedLine parsedLine = reader.getParser().parse(line, 0);
+                final String commandName = parsedLine.word();
+
+                if (commandStore.hasCommand(commandName)) {
+                    commandStore.execute(session, commandName);
+                }
+
+                terminalWriter.println("line = " + String.join(", ", parsedLine.words()));
             }
         } catch (UserInterruptException ignore) {
             // ignore

src/main/java/mc/server/shell/CommandStore.java

@@ -0,0 +1,50 @@
+package mc.server.shell;
+
+import org.jline.builtins.Builtins.CommandInput;
+import org.jline.builtins.Builtins.CommandMethods;
+import org.jline.builtins.CommandRegistry;
+import org.jline.builtins.Completers.SystemCompleter;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
+public class CommandStore implements CommandRegistry {
+
+    private final Map<String, CommandMethods> commandExecutors = new HashMap<>();
+
+    public void register(String name, CommandMethods commandMethods) {
+        commandExecutors.put(name, commandMethods);
+    }
+
+    public void execute(CommandSession session, String command) {
+        commandExecutors.get(command).execute().accept(new CommandInput(command, new Object[0], session));
+    }
+
+    @Override
+    public Set<String> commandNames() {
+        return commandExecutors.keySet();
+    }
+
+    @Override
+    public Map<String, String> commandAliases() {
+        return Collections.emptyMap();
+    }
+
+    @Override
+    public boolean hasCommand(String command) {
+        return commandExecutors.containsKey(command);
+    }
+
+    @Override
+    public SystemCompleter compileCompleters() {
+        SystemCompleter systemCompleter = new SystemCompleter();
+
+        commandExecutors.forEach((name, commandMethods) ->
+                systemCompleter.add(name, commandMethods.compileCompleter().apply(name)));
+        systemCompleter.addAliases(commandAliases());
+
+        return systemCompleter;
+    }
+}