如何使用Erlang文件:read_file_info权限/模式信息? [英] How to use Erlang file:read_file_info permissions/mode info?

问题描述

file:read_file_info/1的Erlang文档指出文件许可权是和"和其他位...可以被设置"，而不是灌输信心.而且，Google并不是我的朋友.

The Erlang docs for file:read_file_info/1 state "file permissions [are] the sum" and "other bits...may be set", not instilling confidence. And, Google has not been my friend here.

我希望采用file:read_file_info/1返回的模式，例如33188，在Linux机器上，并将其转换为更易于理解和/或识别的内容，例如rw-r--r--或644.

I'm looking to take the mode returned by file:read_file_info/1, e.g. 33188, on a Linux machine and convert it into something more human readable and/or recognizable, like rw-r--r-- or 644.

任何提示，链接或指示都将不胜感激.

Any tips, links, or directions greatly appreciated.

推荐答案

简而言之:

io_lib:format("~.8B", [Mode]).

...或:

io_lib:format("~.8B", [Mode band 8#777]).

对于Mode = 33204，这两个将分别为您提供:["100664"]和["664"].

For Mode = 33204 these two will give you respectively: ["100664"] and ["664"].

很长的路要走

print(Mode) ->
    print(Mode band 8#777, []).

print(0, Acc) when length(Acc) =:= 9 ->
    Acc;
print(N, Acc) ->
    Char = perm(N band 1, length(Acc) rem 3),
    print(N bsr 1, [Char | Acc]).

perm(0, _) ->
    $-;
perm(1, 0) ->
    $x;
perm(1, 1) ->
    $w;
perm(1, 2) ->
    $r.

Mode = 33204的这个(功能print/1)将为您提供结果:"rw-rw-r--".

This one (function print/1) for Mode = 33204 will give you this as result: "rw-rw-r--".

如果不清楚的是什么，我将尝试在提供的摘录中阐述基本知识.

If something was unclear for one, I'll try to expound basic things behind the snippets which I have provided.

正如@macintux已经提到的，33204实际上是八进制数100664的十进制表示形式.这三个最低的八进制数字(664)可能是您所需要的，因此我们按位和具有最大数字的(band)操作，该数字适合三个八进制数字(8#777).这就是为什么短途之路如此之短的原因-您只是告诉erlang将Mode转换为字符串，就好像它是八进制数字一样.

As @macintux mentioned already, the 33204 in fact is a decimal representation of the octal number 100664. These three lowest octal digits (664) there is probably what you need, and so we get them with bitwise and (band) operation with the highest number which fits in three octal digits (8#777). That's why short way is so short - you just tell erlang to convert Mode to string as if it was the octal number.

您提到的第二个表示形式(如rw-rw-r--，是ls吐出的东西)可以很容易地从Mode数字的二进制表示形式再现.请注意，三个八进制数字将恰好为您提供九个二进制数字(8#644 = 2#110110100).实际上，这是字符串rwxrwxrwx，如果相应的数字等于0，则每个元素都用-替换.如果digit是1，则该元素保持不变.

The second representation you've mentioned (like rw-rw-r--, something that ls spits out) is easily reproducible from binary representation of the Mode number. Note that three octal digits will give you exactly nine binary digits (8#644 = 2#110110100). In fact this is the string rwxrwxrwx where each element replaced by - if corresponding digit equals 0. If digit is 1 the element remains untouched.

因此，有一种更简洁的方法可以实现这一目标:

So there is slightly cleaner approach to achieve this:

print(Mode) ->
    print(Mode band 8#777, lists:reverse("rwxrwxrwx"), []).

print(0, [], Acc) ->
    Acc;
print(N, [Char0 | Rest], Acc) ->
    Char = char(N band 1, Char0),
    print(N bsr 1, Rest, [Char | Acc]).

char(0, _) ->
    $-;
char(1, C) ->
    C.

---

我希望你明白这一点.如果您有任何疑问，请随时在评论中提出任何问题.

---

I hope you got the point. Anyway feel free to ask any questions in comments if you doubt.

这篇关于如何使用Erlang文件:read_file_info权限/模式信息?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！