常用的 git 说明见 [git 使用说明](./git.md) 。本文记录一些底层 git 技术。

### clone 本地仓库
```bash
$ git clone /home/git/repositories/801/038/000/38801.git
```

### 查看object文件的内容
使用 `git cat-file` 可以查看 `object` 文件的内容，但是查看的内容是转换过的：

```bash
$ git cat-file -p aa548c4d7910229712ba3a41e74c6db872e8ab64
100644 blob c30106543ed8f32af334362fa82e3a4ad71ef20f	home.md
```

可以使用 [zlib-flate](http://manpages.ubuntu.com/manpages/trusty/man1/zlib-flate.1.html) 命令解压看到真实内容：

```bash
$ zlib-flate -uncompress < .git/objects/aa/548c4d7910229712ba3a41e74c6db872e8ab64 | hexdump -C
00000000  74 72 65 65 20 33 35 00  31 30 30 36 34 34 20 68  |tree 35.100644 h|
00000010  6f 6d 65 2e 6d 64 00 c3  01 06 54 3e d8 f3 2a f3  |ome.md....T>..*.|
00000020  34 36 2f a8 2e 3a 4a d7  1e f2 0f                 |46/..:J....|
0000002b
```

> tree 对象 文件格式请看：[tree 对象](https://juejin.im/post/6874840619332665357#heading-16)。
> 需要安装 qpdf 才能正常使用 [zlib-flate](http://manpages.ubuntu.com/manpages/trusty/man1/zlib-flate.1.html) 命令：`apt install qpdf` 。

### git cat-file
查看objects文件。
**说明**
```bash
usage: git cat-file (-t [--allow-unknown-type] | -s [--allow-unknown-type] | -e | -p | <type> | --textconv | --filters) [--path=<path>] <object>
   or: git cat-file (--batch | --batch-check) [--follow-symlinks] [--textconv | --filters]

<type> can be one of: blob, tree, commit, tag
    -t                    show object type
    -s                    show object size
    -e                    exit with zero when there's no error
    -p                    pretty-print object's content
    --textconv            for blob objects, run textconv on object's content
    --filters             for blob objects, run filters on object's content
    --path <blob>         use a specific path for --textconv/--filters
    --allow-unknown-type  allow -s and -t to work with broken/corrupt objects
    --buffer              buffer --batch output
    --batch[=<format>]    show info and content of objects fed from the standard input
    --batch-check[=<format>]
                          show info about objects fed from the standard input
    --follow-symlinks     follow in-tree symlinks (used with --batch or --batch-check)
    --batch-all-objects   show all objects with --batch or --batch-check
```
**示例**
```bash
# 查看objects文件类型
$ git cat-file -t 56ec1a0729533fbd8d38b7964b6f8ca2cace70ba
commit

# 查看objects文件大小
$ git cat-file -s 56ec1a0729533fbd8d38b7964b6f8ca2cace70ba
243

# 查看objects文件（格式化）内容
$ git cat-file -p 56ec1a0729533fbd8d38b7964b6f8ca2cace70ba
tree 7f9adb36c3e987d1ca9d40ba538afd8cbc74e942
parent cf22ff3d15d718603f93c36f13d848e00d841def
author chenan.xxw <chenan.xxw@alibaba-inc.com> 1599545250 +0800
committer chenan.xxw <chenan.xxw@alibaba-inc.com> 1599545250 +0800

update README.md

# 也可以通过 tag 或 branch 名称查看 object 文件
$ git cat-file -t v0.1.0
tag
$ git cat-file -p v0.1.0
object c5b97d5ae6c19d5c5df71a34c7fbeeda2479ccbc
type commit
tag v0.1.0
tagger Scott Chacon <schacon@gmail.com> 1290556430 -0800

tagging initial release of libgit2
```