Git之旅 - 子命令与设计哲学

ivansli 2021/11/19 281℃ 0

如果有人让你猜Git总共有多少子命令,你可能会在思索一番之后说:可能几十个吧(虽然常用的不超过10个)。那么,当我告诉你大概有170多个时,你会是什么反应呢?

1. 所有Git子命令

Git版本号(这里所用版本号:2.22.0)

~ git version
git version 2.22.0

查看子命令的几种方法

1.1 通过帮助信息

git help
git help -a // (显示可用的子命令)
git help -g // (最常用的 Git 向导)

1.2 直接查看子命令

//Linux

ls -lF /usr/local/git/libexec/git-core | wc -l

//mac
ls -lF /usr/local/Cellar/git/2.22.0_1/libexec/git-core |wc -l

目前,2.22.0版本子命令数:170多个

2. Git子命令

下图中是常用的Git命令

2.1 几个Git底层命令

  • 保存数据并生成sha-1字符
    echo xxx | git hash-object -w --stdin
    git hash-object filename
  • 查看对象类型
    git cat-file -t sha1
  • 查看对象内容
    git cat-file -p sha-1
  • 显示暂存区目录树,第三个字段是暂存区编号
    git ls-files -s(--stage)
  • 查看HEAD指向的目录树,-l参数显示文件大小
    git ls-tree -l -r -t HEAD
  • 查看打包的对象文件
    git verify-pack -v .git/objects/pack/pack-xxxxxxxxxxxx.idx
  • 数据对象打包
    git gc
  • 文件索引添加到暂存区
    git update-index --add --cacheinfo 100644 9f358a4addefcab294b83e4282bfef1f9625a249b
  • 生成一棵树(tree对象)
    git write-tree
  • 生成commit对象,并指向一棵树
    echo "second commit " | git commit-tree 43e82 -p c760d78
  • 查看当前所有分支指向的版本号
    git show-ref

2.2 剖析Git的3把刷子与1枚军刀

3把刷子

ls //查看当前工作区
ls-files //查看当前暂存区
ls-tree //查看当前仓库区

1枚瑞士军刀

cat-file //查看git对象

3. 为什么这么多子命令?

这要从两方面分析:

  1. 设计哲学
  2. 源码

3.1 设计哲学角度

linux

一切皆文件
单一目的的小程序
组合小程序完成复杂任务
文本文件保存配置信息
......

git

还是文件 (对象)
子命令 (小程序)
.gitconfig .gitignore (配置信息)
......

Linux kernel与Git都来自同一人之手,所以你懂的...

3.2 源码角度

static struct cmd_struct commands[] = {
    { "add", cmd_add, RUN_SETUP | NEED_WORK_TREE },
    { "am", cmd_am, RUN_SETUP | NEED_WORK_TREE },
    { "annotate", cmd_annotate, RUN_SETUP | NO_PARSEOPT },
    { "apply", cmd_apply, RUN_SETUP_GENTLY },
    { "archive", cmd_archive, RUN_SETUP_GENTLY },
    { "bisect--helper", cmd_bisect__helper, RUN_SETUP },
    { "blame", cmd_blame, RUN_SETUP },
    { "branch", cmd_branch, RUN_SETUP | DELAY_PAGER_CONFIG },
    { "bundle", cmd_bundle, RUN_SETUP_GENTLY | NO_PARSEOPT },
    { "cat-file", cmd_cat_file, RUN_SETUP },
    { "check-attr", cmd_check_attr, RUN_SETUP },
    { "check-ignore", cmd_check_ignore, RUN_SETUP | NEED_WORK_TREE },
    { "check-mailmap", cmd_check_mailmap, RUN_SETUP },
    { "check-ref-format", cmd_check_ref_format, NO_PARSEOPT  },
    { "checkout", cmd_checkout, RUN_SETUP | NEED_WORK_TREE },
    { "checkout-index", cmd_checkout_index,
        RUN_SETUP | NEED_WORK_TREE},
    { "cherry", cmd_cherry, RUN_SETUP },
    { "cherry-pick", cmd_cherry_pick, RUN_SETUP | NEED_WORK_TREE },
    { "clean", cmd_clean, RUN_SETUP | NEED_WORK_TREE },
    { "clone", cmd_clone },
    { "column", cmd_column, RUN_SETUP_GENTLY },
    { "commit", cmd_commit, RUN_SETUP | NEED_WORK_TREE },
    { "commit-graph", cmd_commit_graph, RUN_SETUP },
    { "commit-tree", cmd_commit_tree, RUN_SETUP | NO_PARSEOPT },
    { "config", cmd_config, RUN_SETUP_GENTLY | DELAY_PAGER_CONFIG },
    { "count-objects", cmd_count_objects, RUN_SETUP },
    { "credential", cmd_credential, RUN_SETUP_GENTLY | NO_PARSEOPT },
    { "describe", cmd_describe, RUN_SETUP },
    { "diff", cmd_diff, NO_PARSEOPT },
    { "diff-files", cmd_diff_files, RUN_SETUP | NEED_WORK_TREE | NO_PARSEOPT },
    { "diff-index", cmd_diff_index, RUN_SETUP | NO_PARSEOPT },
    { "diff-tree", cmd_diff_tree, RUN_SETUP | NO_PARSEOPT },
    { "difftool", cmd_difftool, RUN_SETUP_GENTLY },
    { "env--helper", cmd_env__helper },
    { "fast-export", cmd_fast_export, RUN_SETUP },
    { "fetch", cmd_fetch, RUN_SETUP },
    { "fetch-pack", cmd_fetch_pack, RUN_SETUP | NO_PARSEOPT },
    { "fmt-merge-msg", cmd_fmt_merge_msg, RUN_SETUP },
    { "for-each-ref", cmd_for_each_ref, RUN_SETUP },
    { "format-patch", cmd_format_patch, RUN_SETUP },
    { "fsck", cmd_fsck, RUN_SETUP },
    { "fsck-objects", cmd_fsck, RUN_SETUP },
    { "gc", cmd_gc, RUN_SETUP },
    { "get-tar-commit-id", cmd_get_tar_commit_id, NO_PARSEOPT },
    { "grep", cmd_grep, RUN_SETUP_GENTLY },
    { "hash-object", cmd_hash_object },
    { "help", cmd_help },
    { "index-pack", cmd_index_pack, RUN_SETUP_GENTLY | NO_PARSEOPT },
    { "init", cmd_init_db },
    { "init-db", cmd_init_db },
    { "interpret-trailers", cmd_interpret_trailers, RUN_SETUP_GENTLY },
    { "log", cmd_log, RUN_SETUP },
    { "ls-files", cmd_ls_files, RUN_SETUP },
    { "ls-remote", cmd_ls_remote, RUN_SETUP_GENTLY },
    { "ls-tree", cmd_ls_tree, RUN_SETUP },
    { "mailinfo", cmd_mailinfo, RUN_SETUP_GENTLY | NO_PARSEOPT },
    { "mailsplit", cmd_mailsplit, NO_PARSEOPT },
    { "merge", cmd_merge, RUN_SETUP | NEED_WORK_TREE },
    { "merge-base", cmd_merge_base, RUN_SETUP },
    { "merge-file", cmd_merge_file, RUN_SETUP_GENTLY },
    { "merge-index", cmd_merge_index, RUN_SETUP | NO_PARSEOPT },
    { "merge-ours", cmd_merge_ours, RUN_SETUP | NO_PARSEOPT },
    { "merge-recursive", cmd_merge_recursive, RUN_SETUP | NEED_WORK_TREE | NO_PARSEOPT },
    { "merge-recursive-ours", cmd_merge_recursive, RUN_SETUP | NEED_WORK_TREE | NO_PARSEOPT },
    { "merge-recursive-theirs", cmd_merge_recursive, RUN_SETUP | NEED_WORK_TREE | NO_PARSEOPT },
    { "merge-subtree", cmd_merge_recursive, RUN_SETUP | NEED_WORK_TREE | NO_PARSEOPT },
    { "merge-tree", cmd_merge_tree, RUN_SETUP | NO_PARSEOPT },
    { "mktag", cmd_mktag, RUN_SETUP | NO_PARSEOPT },
    { "mktree", cmd_mktree, RUN_SETUP },
    { "multi-pack-index", cmd_multi_pack_index, RUN_SETUP_GENTLY },
    { "mv", cmd_mv, RUN_SETUP | NEED_WORK_TREE },
    { "name-rev", cmd_name_rev, RUN_SETUP },
    { "notes", cmd_notes, RUN_SETUP },
    { "pack-objects", cmd_pack_objects, RUN_SETUP },
    { "pack-redundant", cmd_pack_redundant, RUN_SETUP | NO_PARSEOPT },
    { "pack-refs", cmd_pack_refs, RUN_SETUP },
    { "patch-id", cmd_patch_id, RUN_SETUP_GENTLY | NO_PARSEOPT },
    { "pickaxe", cmd_blame, RUN_SETUP },
    { "prune", cmd_prune, RUN_SETUP },
    { "prune-packed", cmd_prune_packed, RUN_SETUP },
    { "pull", cmd_pull, RUN_SETUP | NEED_WORK_TREE },
    { "push", cmd_push, RUN_SETUP },
    { "range-diff", cmd_range_diff, RUN_SETUP | USE_PAGER },
    { "read-tree", cmd_read_tree, RUN_SETUP | SUPPORT_SUPER_PREFIX},
    { "rebase", cmd_rebase, RUN_SETUP | NEED_WORK_TREE },
    { "rebase--interactive", cmd_rebase__interactive, RUN_SETUP | NEED_WORK_TREE },
    { "receive-pack", cmd_receive_pack },
    { "reflog", cmd_reflog, RUN_SETUP },
    { "remote", cmd_remote, RUN_SETUP },
    { "remote-ext", cmd_remote_ext, NO_PARSEOPT },
    { "remote-fd", cmd_remote_fd, NO_PARSEOPT },
    { "repack", cmd_repack, RUN_SETUP },
    { "replace", cmd_replace, RUN_SETUP },
    { "rerere", cmd_rerere, RUN_SETUP },
    { "reset", cmd_reset, RUN_SETUP },
    { "restore", cmd_restore, RUN_SETUP | NEED_WORK_TREE },
    { "rev-list", cmd_rev_list, RUN_SETUP | NO_PARSEOPT },
    { "rev-parse", cmd_rev_parse, NO_PARSEOPT },
    { "revert", cmd_revert, RUN_SETUP | NEED_WORK_TREE },
    { "rm", cmd_rm, RUN_SETUP },
    { "send-pack", cmd_send_pack, RUN_SETUP },
    { "shortlog", cmd_shortlog, RUN_SETUP_GENTLY | USE_PAGER },
    { "show", cmd_show, RUN_SETUP },
    { "show-branch", cmd_show_branch, RUN_SETUP },
    { "show-index", cmd_show_index },
    { "show-ref", cmd_show_ref, RUN_SETUP },
    { "stage", cmd_add, RUN_SETUP | NEED_WORK_TREE },
    /*
     * NEEDSWORK: Until the builtin stash is thoroughly robust and no
     * longer needs redirection to the stash shell script this is kept as
     * is, then should be changed to RUN_SETUP | NEED_WORK_TREE
     */
    { "stash", cmd_stash },
    { "status", cmd_status, RUN_SETUP | NEED_WORK_TREE },
    { "stripspace", cmd_stripspace },
    { "submodule--helper", cmd_submodule__helper, RUN_SETUP | SUPPORT_SUPER_PREFIX | NO_PARSEOPT },
    { "switch", cmd_switch, RUN_SETUP | NEED_WORK_TREE },
    { "symbolic-ref", cmd_symbolic_ref, RUN_SETUP },
    { "tag", cmd_tag, RUN_SETUP | DELAY_PAGER_CONFIG },
    { "unpack-file", cmd_unpack_file, RUN_SETUP | NO_PARSEOPT },
    { "unpack-objects", cmd_unpack_objects, RUN_SETUP | NO_PARSEOPT },
    { "update-index", cmd_update_index, RUN_SETUP },
    { "update-ref", cmd_update_ref, RUN_SETUP },
    { "update-server-info", cmd_update_server_info, RUN_SETUP },
    { "upload-archive", cmd_upload_archive, NO_PARSEOPT },
    { "upload-archive--writer", cmd_upload_archive_writer, NO_PARSEOPT },
    { "upload-pack", cmd_upload_pack },
    { "var", cmd_var, RUN_SETUP_GENTLY | NO_PARSEOPT },
    { "verify-commit", cmd_verify_commit, RUN_SETUP },
    { "verify-pack", cmd_verify_pack },
    { "verify-tag", cmd_verify_tag, RUN_SETUP },
    { "version", cmd_version },
    { "whatchanged", cmd_whatchanged, RUN_SETUP },
    { "worktree", cmd_worktree, RUN_SETUP | NO_PARSEOPT },
    { "write-tree", cmd_write_tree, RUN_SETUP },
};

int cmd_main(int argc, const char **argv)
{
    const char *cmd;
    int done_help = 0;

    cmd = argv[0];
    if (!cmd)
        cmd = "git-help";
    else {
        const char *slash = find_last_dir_sep(cmd);
        if (slash)
            cmd = slash + 1;
    }

    trace_command_performance(argv);

    /*
     * "git-xxxx" is the same as "git xxxx", but we obviously:
     *
     *  - cannot take flags in between the "git" and the "xxxx".
     *  - cannot execute it externally (since it would just do
     *    the same thing over again)
     *
     * So we just directly call the builtin handler, and die if
     * that one cannot handle it.
     */
    if (skip_prefix(cmd, "git-", &cmd)) {
        argv[0] = cmd;
        handle_builtin(argc, argv);
        die(_("cannot handle %s as a builtin"), cmd);
    }

可以看出来,但凡带 "git-" 前缀的命令与去掉前缀作为git的子命令是一样的。

反应在代码中,每一个命令又是一个单独的文件存在。

如此以来,复杂的git就化整为零,靠着众多子命令单独的功能,实现一个复杂的版本控制系统。

看来,好的程序员必修的一门课,放在第一位的绝对是:哲学。

Git

评论啦~