How to read the mode field of git-ls-tree's output

$ git ls-tree fb3a8bdd0ce
100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c    .gitignore
100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d    .mailmap
100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3    COPYING
040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745    Documentation
100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200    GIT-VERSION-GEN
100644 blob 289b046a443c0647624607d471289b2c7dcd470b    INSTALL
100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1    Makefile
100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52    README
...

I know the last 3 oct digits are file mode, but what are the first 3 digits for? I can't find it out in git user's manual.

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最佳答案

这6位数字使用经典的 UNIX 符号显示文件模式。 First two digits show file type, the third one is about set-uid/set-gid/sticky bits, and you know the last three.

下面是 man 2 stat如何在我的 GNU/Linux 系统上记录它:

   The following flags are defined for the st_mode field:


S_IFMT     0170000   bit mask for the file type bit fields
S_IFSOCK   0140000   socket
S_IFLNK    0120000   symbolic link
S_IFREG    0100000   regular file
S_IFBLK    0060000   block device
S_IFDIR    0040000   directory
S_IFCHR    0020000   character device
S_IFIFO    0010000   FIFO
S_ISUID    0004000   set UID bit
S_ISGID    0002000   set-group-ID bit (see below)
S_ISVTX    0001000   sticky bit (see below)
S_IRWXU    00700     mask for file owner permissions
S_IRUSR    00400     owner has read permission
S_IWUSR    00200     owner has write permission
S_IXUSR    00100     owner has execute permission
S_IRWXG    00070     mask for group permissions
S_IRGRP    00040     group has read permission
S_IWGRP    00020     group has write permission
S_IXGRP    00010     group has execute permission
S_IRWXO    00007     mask for permissions for others (not in group)
S_IROTH    00004     others have read permission
S_IWOTH    00002     others have write permission
S_IXOTH    00001     others have execute permission
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来自 Git index-format.txt文件，关于模式:

32-bit mode, split into (high to low bits)


4-bit object type
valid values in binary are 1000 (regular file), 1010 (symbolic link)
and 1110 (gitlink)


3-bit unused


9-bit unix permission. Only 0755 and 0644 are valid for regular files.
Symbolic links and gitlinks have value 0 in this field.

此外，根据 fsck.c fsck_tree方法的指示，目录对象类型(二进制0100)和组可写(0664权限)常规文件也是允许的。常规的不可执行的组可写文件是 Git 早期版本支持的非标准模式。

这使得有效模式(作为二进制和八进制) :

  • 目录
  • 1000000110100100(100644) : 常规的不可执行文件
  • 1000000110110100(100664) : 常规的不可执行的组可写文件
  • 1000000111101101 (100755): Regular executable file
  • 1010000000000000(120000) : 符号链接
  • 1110000000000000(160000) : Gitlink

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