diff --git a/barg.js b/barg.js
index 5ffa56c..2c9565c 100644
--- a/barg.js
+++ b/barg.js
@@ -51,12 +51,11 @@ function tokenize(input) {
 
 function parse_input(spec, input) {
   const tokens = tokenize(input);
-  const values = {};
 
   const schema = {};
   const alias_map = {};
 
-  let position = 0;
+  let position = [null, 0];
   let level = 1;
   let commands = ["_"];
 
@@ -86,7 +85,6 @@ function parse_input(spec, input) {
           // Schema
           schema[ref(name, "type")] = "command";
           schema[ref(name, "help")] = help;
-          schema[ref(name, "args")] = "";
 
           // Alias
           for (const alias of aliases) {
@@ -96,7 +94,7 @@ function parse_input(spec, input) {
           // Control
           commands.push(name);
           level += 1;
-          position = 0;
+          position[level] = 0;
           break;
         }
         case "end": {
@@ -108,26 +106,21 @@ function parse_input(spec, input) {
           let aliases = elements.shift().split(",");
           let name = aliases[0];
 
-          const entry = { required: false, kind: "positional" };
+          const entry = { name, dest: name, required: false, kind: "positional" };
           for (const element of elements) {
             const [attribute, attr_value] = element.split(":");
-            let default_value;
 
             if (attribute === "required") entry.required = true;
             else if (attribute === "repeatable") entry.repeatable = true;
             else if (attribute === "help") entry.help = attr_value;
             else if (attribute === "dest") entry.dest = attr_value;
             else if (attribute === "type") entry.kind = attr_value;
-            else if (attribute === "default") default_value = attr_value;
-
-            // Defaults
-            if (entry.dest === undefined) entry.dest = name;
-            if (entry.value === undefined) entry.value = default_value;
+            else if (attribute === "default") entry.value = attr_value;
           }
 
           // Alias
           if (entry.kind === "positional") {
-            name = String(position++);
+            name = String(position[level]++);
             aliases = [`pos::${name}`];
           } else if (entry.kind === "rest") {
             aliases = ["__rest"];
@@ -148,7 +141,11 @@ function parse_input(spec, input) {
           }
 
           // Register arg to command
-          schema[ref("args")] += `${name},`;
+          if (schema[ref("args")]) {
+            schema[ref("args")] += `,${name}`;
+          } else {
+            schema[ref("args")] = `${name}`;
+          }
 
           break;
         }
@@ -159,7 +156,7 @@ function parse_input(spec, input) {
 
     commands = ["_"];
     level = 1;
-    position = 0;
+    position = [null, 0];
   }
 
   function next_token_value() {
@@ -172,7 +169,7 @@ function parse_input(spec, input) {
   }
 
   generate_schema();
-  log({ schema, alias_map });
+  // log({ schema, alias_map });
 
   while (tokens.length > 0) {
     const token = take_one(tokens);
@@ -194,9 +191,9 @@ function parse_input(spec, input) {
 
       if (!entry_ref && level === commands.length && token_type === "unk") {
         // Positional arguments are valid only for the latest command
-        entry_ref = get_entry_ref(`pos::${position}`);
+        entry_ref = get_entry_ref(`pos::${position[level]}`);
         if (entry_ref) {
-          position += 1;
+          position[level] += 1;
         }
       }
 
@@ -208,10 +205,9 @@ function parse_input(spec, input) {
       const entry_type = get_entry_item(entry_ref, "type");
       if (entry_type === "command") {
         commands.push(token_key);
+        position.push(0);
       } else if (entry_type === "argument") {
         const kind = get_entry_item(entry_ref, "kind");
-        const dest = get_entry_item(entry_ref, "dest");
-        const default_value = get_entry_item(entry_ref, "value");
 
         let value;
         if (kind === "flag") value = true;
@@ -220,7 +216,7 @@ function parse_input(spec, input) {
         else if (kind === "rest") value = token_key;
         else throw new Error(`Invalid attribute type: '${kind}'`);
 
-        values[dest] = value;
+        schema[join(entry_ref, "value")] = value;
       }
 
       found = true;
@@ -228,7 +224,35 @@ function parse_input(spec, input) {
     }
 
     if (!found) {
-      console.log(`(Skipping invalid argument: '${token_key}'`);
+      console.log(`> Skipping invalid argument: (${token_type}) '${token_key}'`);
+    }
+  }
+
+  // Check required
+  const values = {};
+  let id = "";
+  for (const command of commands) {
+    id = join(id, command);
+    let command_args = schema[join(id, "args")];
+    if (!command_args) {
+      continue;
+    }
+
+    for (const arg of command_args.split(",")) {
+      const name = schema[join(id, arg, "name")];
+      const dest = schema[join(id, arg, "dest")];
+      const value = schema[join(id, arg, "value")];
+      const required = schema[join(id, arg, "required")];
+
+      if (value === undefined && required) {
+        throw new Error(`Argument '${name}' is required in command '${command}'`);
+      }
+
+      if (values[dest] !== undefined) {
+        values[`${command}_${dest}`] = value;
+      } else {
+        values[dest] = value;
+      }
     }
   }
 
@@ -237,11 +261,19 @@ function parse_input(spec, input) {
   return values;
 }
 
+function parse_input_wrap(spec, input) {
+  try {
+    parse_input(spec, input);
+  } catch (error) {
+    console.error(`Error: ${error.message}`);
+  }
+}
+
 const SPEC = [
   "command;build;Build a dev container",
   "argument;from;type:option;dest:from_name;help:Name of the base container",
   "argument;name;type:positional;required;help:Name of the container",
-  "argument;name;type:option;required;help:Name of the container",
+  "argument;nametwo;help:Name of the container",
   "argument;image,i;type:option;required;dest:image_name;help:Base image",
   "argument;include,I;type:option;repeatable;dest:include_paths;help:Include paths",
   "argument;verbose,v;type:flag;repeatable;default:0;help:Increase verbosity (-v, -vv, ...)",
@@ -253,7 +285,6 @@ const SPEC = [
   "argument;name;required;help:Building container name",
   "argument;cmd;type:rest;dest:cmd_rest;help:Command and args to run inside the container",
   "end",
-  "argument;external;required;help:Name of the external container",
   "end",
   "command;stop;Stop a dev container",
   "argument;name;type:positional;required;help:Name of the container",
@@ -262,15 +293,17 @@ const SPEC = [
 ];
 
 const INPUTS = [
-  "dev build --from base-dev --image node:18 --include src --include test -v -v -q mycontainer -- npm run start",
-  "dev build container --dev --name webapp externalContainer",
-  "dev build container --dev --name webapp externalContainer -- echo hi",
+  "dev build -i myimage buildtwo --from base-dev --image node:18 --include src --include test -v -v -q mycontainer -- npm run start",
+  "dev build buildname container -i myimage --dev --name webapp externalContainer",
+  "dev build --image debian mybox container --dev --name webapp externalContainer -- echo hi",
   "dev stop mycontainer --kill",
+  "dev stop mycontainer --kill -- not specified one",
   "dev build --from alpine --image node:20 mybox -- echo hi",
+  "dev build --aaaaa --from alpine --image node:20 --bbbbb orb mybox ccccc -- echo hi",
 ];
 
 INPUTS.forEach((input) => {
   console.log("\n\n------------------------\n");
   console.log("> ", input);
-  parse_input(SPEC, input);
+  parse_input_wrap(SPEC, input);
 });