diff --git a/src/expansion/expansion.c b/src/expansion/expansion.c
index e69de29..406c00b 100644
--- a/src/expansion/expansion.c
+++ b/src/expansion/expansion.c
@@ -0,0 +1,87 @@
+#include <ctype.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "../utils/ast/ast.h"
+
+// static size_t var_len(char *start)
+// {
+//     char *iter = start;
+//     while (*iter != ' ' && *iter != 0)
+//         *iter++;
+//     return iter - start;
+// }
+
+struct ast_cmd *expand(struct ast_cmd *cmd)
+{
+    if (cmd == NULL)
+        return NULL;
+
+    bool in_quotes = false;
+    char *str;
+    size_t len;
+    struct list *l = cmd->cmd;
+
+    while (l != NULL)
+    {
+        in_quotes = false;
+        str = (char *)l->data;
+        len = strlen(str);
+
+        for (size_t i = 0; str[i] != '\0'; i++)
+        {
+            if (in_quotes)
+            {
+                // do nothing
+            }
+            else if (str[i] == '\'')
+            {
+                in_quotes = !in_quotes;
+                memmove(&str[i], &str[i + 1], strlen(&str[i + 1]) + 1);
+            }
+            else if (str[i] == '$' && str[i + 1] != 0 && !isspace(str[i + 1]))
+            {
+                // size_t len = var_len(str + i + 1);
+                // char *end = str + i + len + 1;
+                // char c = *end;
+                // *end = 0;
+                // printf("var: %s\n", str + i + 1);
+                // *end = c;
+            }
+        }
+
+        if (in_quotes)
+        {
+            // error: quote not closed
+        }
+
+        if (len != strlen(str))
+        {
+            char *new_str = realloc(str, strlen(str) + 1);
+            if (new_str == NULL)
+            {
+                // error: realloc fail
+            }
+            l->data = new_str;
+        }
+
+        l = l->next;
+    }
+    return cmd;
+}
+
+// int main()
+// {
+//     printf("Expansion module test\n");
+//     struct ast_cmd ast_cmd;
+//     // char str[] = "echo Hello $?";
+//     char str[] = "echo Hello $AE86";
+//     ast_cmd.cmd = list_append(NULL, str);
+
+//     struct ast_cmd *cmd2 = expand(&ast_cmd);
+//     printf("cmd2: %s\n", (char *)cmd2->cmd->data);
+
+//     return 0;
+// }