add systemctl, exit and echo commands

src/emulator/commands/echo.js

@@ -0,0 +1,36 @@
+const { Terminal } = require("xterm");
+
+/**
+ * 
+ * @param {string[]} argv 
+ * @param {Terminal} terminal 
+ */
+module.exports = (argv, terminal) => {
+    if (argv.indexOf('--help') != -1) {
+        terminal.write(
+`Usage: ${argv[0]} [-e] [MESSAGE]
+Print a line of text into terminal.
+    -e \t Enable parsing of backslash escapes`
+        );
+        return;
+    }
+
+    let args = [...argv];
+    args.shift();
+
+    // remove -e
+    if (args.indexOf('-e') != -1)
+        args.splice(args.indexOf('-e'), 1)
+
+    let text = args.join(' ');
+
+    if (argv.indexOf('-e') != -1) {
+        try {
+            text = JSON.parse(`"${text}"`);
+        } catch (err) {
+            terminal.write(`${argv[0]}: can't parse string: ${err}`);
+        }
+    }
+
+    terminal.writeln(text);
+}

src/emulator/commands/exit.js

@@ -0,0 +1,10 @@
+const { Terminal } = require("xterm");
+
+/**
+ * 
+ * @param {string[]} argv 
+ * @param {Terminal} terminal 
+ */
+module.exports = (argv, terminal) => {
+    terminal.writeln(`${argv[0]}: not supported`);
+}

src/emulator/commands/index.js

@@ -12,6 +12,9 @@ let cmds = {
     'ps': require('./ps'),
     'clear': require('./clear'),
     'rm': require('./rm'),
+    'echo': require('./echo'),
+    'exit': require('./exit'),
+    'systemctl': require('./systemctl'),
 
 
     'guide': require('./guide'),

src/emulator/commands/systemctl.js

@@ -0,0 +1,10 @@
+const { Terminal } = require("xterm");
+
+/**
+ * 
+ * @param {string[]} argv 
+ * @param {Terminal} terminal 
+ */
+module.exports = (argv, terminal) => {
+    terminal.writeln(`${argv[0]}: systemd is bad`);
+}