diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 9d05f4d..b7ce470 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -23,6 +23,5 @@ jobs:
 
       - name: Run tests
         run: |
-          cd xgit
-          coverage run -m pytest .
+          coverage run -m pytest xgit
           coverage report -m
diff --git a/.gitignore b/.gitignore
index 0d83276..45a8579 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,4 @@ __pycache__
 .mypy_cache
 *.egg-info/
 .pytest_cache/
+.coverage
diff --git a/xgit/cli.py b/xgit/cli.py
index 19302b0..7363af1 100644
--- a/xgit/cli.py
+++ b/xgit/cli.py
@@ -1,6 +1,6 @@
 import typer
 
-from xgit.commands import init, cat_file, hash_object
+from xgit.commands import init, cat_file, ls_files, hash_object
 
 app = typer.Typer(add_completion=False, rich_markup_mode="markdown")
 
@@ -8,6 +8,7 @@
 app.command()(hash_object.hash_object)
 app.command()(init.init)
 app.command()(cat_file.cat_file)
+app.command()(ls_files.ls_files)
 
 
 def main():
diff --git a/xgit/commands/ls_files.py b/xgit/commands/ls_files.py
new file mode 100644
index 0000000..766d5a0
--- /dev/null
+++ b/xgit/commands/ls_files.py
@@ -0,0 +1,26 @@
+from pathlib import Path
+
+import typer
+from typer import Option
+from typing_extensions import Annotated
+
+from xgit.types.index import get_index
+from xgit.utils.utils import find_repo
+
+
+def ls_files(
+    full_name: Annotated[bool, Option("--full-name", help="输出相对于项目根目录，而非当前目录")] = False,
+):
+    """
+    输出 index 中在当前目录下的所有文件
+    """
+    index = get_index()
+    for entry in index.entries:
+        f = find_repo() / entry.file_name
+        cwd = Path.cwd()
+
+        if f.is_relative_to(cwd):
+            if full_name:
+                typer.echo(entry.file_name)
+            else:
+                typer.echo(f.relative_to(cwd))
diff --git a/xgit/commands/update_index.py b/xgit/commands/update_index.py
new file mode 100644
index 0000000..32cac84
--- /dev/null
+++ b/xgit/commands/update_index.py
@@ -0,0 +1,23 @@
+from pathlib import Path
+
+import typer
+from typer import Option, Argument
+from typing_extensions import Annotated, Optional
+
+from xgit.types.index import get_index
+from xgit.utils.utils import find_repo
+
+def update_index(
+    files: Annotated[Optional[list[str]], Argument(help="要更新的文件")] = None,
+    add: Annotated[bool, Option("--add", help="如果文件在暂存区中不存在，则加入暂存区")] = False,
+    remove: Annotated[bool, Option("--remove", help="如果文件在暂存区存在，但在本地不存在，则从暂存区移除")] = False,
+    force_remove: Annotated[bool, Option("--force-remove", help="从暂存区移除文件，即使文件在本地存在")] = False,
+    refresh: Annotated[bool, Option("--refresh", help="刷新暂存区中的文件状态")] = False,
+    verbose: Annotated[bool, Option("-v", help="详细输出添加和删除的文件")] = False,
+    cacheinfo: Annotated[str, Option("--cacheinfo", help="与 `--add` 一同使用，用 `<mode>,<object>,<path>` 指定一个 blob 加入暂存区")] = "",
+):
+    """
+    更新暂存区
+    """
+    
+    
\ No newline at end of file
diff --git a/xgit/test/test_ls_files.py b/xgit/test/test_ls_files.py
new file mode 100644
index 0000000..b027d21
--- /dev/null
+++ b/xgit/test/test_ls_files.py
@@ -0,0 +1,19 @@
+import os
+
+from typer.testing import CliRunner
+
+from xgit.test.test_utils import check_same_output
+
+runner = CliRunner()
+
+
+def test_ls_files():
+    assert check_same_output(["ls-files"])
+
+    cwd = os.getcwd()
+    try:
+        os.chdir("xgit")
+        assert check_same_output(["ls-files", "--full-name"])
+        assert check_same_output(["ls-files"])
+    finally:
+        os.chdir(cwd)
diff --git a/xgit/test/test_utils.py b/xgit/test/test_utils.py
index c02da08..4c1fa36 100644
--- a/xgit/test/test_utils.py
+++ b/xgit/test/test_utils.py
@@ -61,7 +61,8 @@ def check_same_output(cmd: list[str]) -> bool:
 
     if git_result.stdout != xgit_stdout:
         logger.info(f"cmd: {cmd}")
-        logger.info(f"stdout not equal: {git_result.stdout} != {xgit_stdout}")
+        logger.info(f"stdout not equal: {git_result.stdout!r}\n!=\n{xgit_stdout!r}")
+        logger.info(f"stdout not equal: {git_result.stdout.decode()}\n!=\n{xgit_stdout.decode()}")
         return False
 
     return True
diff --git a/xgit/types/index.py b/xgit/types/index.py
new file mode 100644
index 0000000..960c474
--- /dev/null
+++ b/xgit/types/index.py
@@ -0,0 +1,228 @@
+import hashlib
+from typing import Optional
+
+from xgit.utils.utils import find_repo
+from xgit.utils.constants import GIT_DIR
+
+
+def print_bytes(data, group_size=4, group_each_line=6):
+    def is_printable(byte):
+        return 32 <= byte <= 126
+
+    byte_each_line = group_size * group_each_line
+
+    n = len(data)
+    for i in range(0, n, byte_each_line):
+        line = data[i : i + byte_each_line]
+        for j in range(0, len(line), group_size):
+            group = line[j : j + group_size]
+            print("0x" + "".join(f"{byte:02x}" for byte in group).upper(), end=" ")
+        print()
+
+        for j in range(0, len(line), group_size):
+            group = line[j : j + group_size]
+            print("   ", end="")
+            print(" ".join(chr(byte) if is_printable(byte) else "*" for byte in group), end=" ")
+        print("\n")
+
+
+class IndexEntry:
+    class Flag:
+        assume_valid: bool
+        extended: bool
+        stage: int
+        name_length: int
+
+        def __init__(self, assume_valid, extended, stage, name_length):
+            self.assume_valid = assume_valid
+            self.extended = extended
+            self.stage = stage
+            self.name_length = name_length
+
+        @staticmethod
+        def from_bytes(data: bytes):
+            assert len(data) == 2
+            flag = int.from_bytes(data, "big")
+            assume_valid = flag & 0x8000 != 0
+            extended = flag & 0x4000 != 0
+            stage = (flag & 0x3000) >> 12
+            name_length = flag & 0x0FFF
+            return IndexEntry.Flag(assume_valid, extended, stage, name_length)
+
+        def to_bytes(self) -> bytes:
+            data = 0
+            if self.assume_valid:
+                data |= 0x8000
+            if self.extended:
+                data |= 0x4000
+            data |= (self.stage << 12) & 0x3000
+            data |= self.name_length
+            return data.to_bytes(2, "big")
+
+    ctime_s: int
+    ctime_ns: int
+    mtime_s: int
+    mtime_ns: int
+    dev: int
+    inode: int
+    mode: int
+    uid: int
+    gid: int
+    file_size: int
+    sha: str
+    flags: Flag
+    extended_flags: Optional[bytes]
+    file_name: str
+
+    def __init__(
+        self,
+        ctime_s,
+        ctime_ns,
+        mtime_s,
+        mtime_ns,
+        dev,
+        inode,
+        mode,
+        uid,
+        gid,
+        file_size,
+        sha,
+        flags,
+        extended_flags,
+        file_name,
+    ):
+        self.ctime_s = ctime_s
+        self.ctime_ns = ctime_ns
+        self.mtime_s = mtime_s
+        self.mtime_ns = mtime_ns
+        self.dev = dev
+        self.inode = inode
+        self.mode = mode
+        self.uid = uid
+        self.gid = gid
+        self.file_size = file_size
+        self.sha = sha
+        self.flags = flags
+        self.extended_flags = extended_flags
+        self.file_name = file_name
+
+    @staticmethod
+    def parse(data: bytes) -> tuple["IndexEntry", bytes]:
+        ctime_s = int.from_bytes(data[:4], "big")
+        ctime_ns = int.from_bytes(data[4:8], "big")
+        mtime_s = int.from_bytes(data[8:12], "big")
+        mtime_ns = int.from_bytes(data[12:16], "big")
+        dev = int.from_bytes(data[16:20], "big")
+        inode = int.from_bytes(data[20:24], "big")
+        mode = int.from_bytes(data[24:28], "big")
+        uid = int.from_bytes(data[28:32], "big")
+        gid = int.from_bytes(data[32:36], "big")
+        file_size = int.from_bytes(data[36:40], "big")
+        sha = data[40:60].hex()
+        flags = IndexEntry.Flag.from_bytes(data[60:62])
+
+        entry_len = 62
+
+        # if flags.extended == True, then there is a 16-bit extended flag
+        if flags.extended:
+            extended_flags = data[62:64]
+            entry_len += 2
+        else:
+            extended_flags = None
+
+        if flags.name_length < 0xFFF:
+            file_name = data[entry_len : entry_len + flags.name_length]
+            assert data[entry_len + flags.name_length] == 0
+            entry_len += flags.name_length + 1
+        else:
+            # if name_length >= 0xFFF, then find `\x00` to get the file name
+            file_name, _ = data[entry_len:].split(b"\x00", maxsplit=1)
+            entry_len += len(file_name) + 1
+
+        entry_len = (entry_len + 7) // 8 * 8  # aligned to 8 bytes
+        rest = data[entry_len:]  # remove padding
+
+        return (
+            IndexEntry(
+                ctime_s,
+                ctime_ns,
+                mtime_s,
+                mtime_ns,
+                dev,
+                inode,
+                mode,
+                uid,
+                gid,
+                file_size,
+                sha,
+                flags,
+                extended_flags,
+                file_name.decode(),
+            ),
+            rest,
+        )
+
+    def to_bytes(self) -> bytes:
+        entry = self.ctime_s.to_bytes(4, "big")
+        entry += self.ctime_ns.to_bytes(4, "big")
+        entry += self.mtime_s.to_bytes(4, "big")
+        entry += self.mtime_ns.to_bytes(4, "big")
+        entry += self.dev.to_bytes(4, "big")
+        entry += self.inode.to_bytes(4, "big")
+        entry += self.mode.to_bytes(4, "big")
+        entry += self.uid.to_bytes(4, "big")
+        entry += self.gid.to_bytes(4, "big")
+        entry += self.file_size.to_bytes(4, "big")
+        entry += bytes.fromhex(self.sha)
+        entry += self.flags.to_bytes()
+        if self.extended_flags is not None:
+            entry += self.extended_flags
+        entry += self.file_name.encode()
+        entry += b"\x00"
+
+        # padding to 8 bytes
+        padding = (8 - len(entry) % 8) % 8
+        entry += b"\x00" * padding
+
+        return entry
+
+
+class Index:
+    version: int
+    entry_count: int
+    entries: list[IndexEntry]
+    extensions: bytes
+
+    def __init__(self, data: Optional[bytes] = None):
+        if data is None:
+            self.version = 2
+            self.entry_count = 0
+            self.entries = []
+        else:
+            self.version = int.from_bytes(data[4:8], "big")
+            self.entry_count = int.from_bytes(data[8:12], "big")
+            self.entries = []
+            data = data[12:]
+            for _ in range(self.entry_count):
+                entry, data = IndexEntry.parse(data)
+                self.entries.append(entry)
+            self.extensions = data[:-20]
+
+    def to_bytes(self) -> bytes:
+        index = b"DIRC"
+        index += self.version.to_bytes(4, "big")
+        index += self.entry_count.to_bytes(4, "big")
+        index += b"".join(entry.to_bytes() for entry in self.entries)
+        index += self.extensions
+        index += hashlib.sha1(index).digest()
+        return index
+
+
+def get_index() -> Index:
+    index_path = find_repo() / GIT_DIR / "index"
+    if not index_path.exists():
+        return Index()
+    with index_path.open("rb") as f:
+        data = f.read()
+        assert data[-20:] == hashlib.sha1(data[:-20]).digest()
+        return Index(data)