A module for calculating access mode of unix files based on the mode_t bit-bucket value.

file_mode_calc.erl

-module(file_mode_calc).

-export([run/0]).

-include_lib("kernel/include/file.hrl").

%% source: https://jameshfisher.github.io/2017/02/24/what-is-mode_t.html

-define(S_IRWXU, 8#0000700).
-define(S_IRUSR, 8#0000400).
-define(S_IWUSR, 8#0000200).
-define(S_IXUSR, 8#0000100).

run() ->
    FilePath = "/tmp/mode/foo",
    {ok, #file_info{mode = Mode}} = file:read_file_info(FilePath),

    ModeBin = integer_to_list(Mode, 2),
    ModeOct = integer_to_list(Mode, 8),
    ModeDec = Mode,

    Read = Mode band ?S_IRUSR,
    Write = Mode band ?S_IWUSR,
    Execute = Mode band ?S_IXUSR,
    ReadWrite = Mode band (?S_IRUSR bor ?S_IWUSR),

    ReadBin = integer_to_list(Read, 2),
    WriteBin = integer_to_list(Write, 2),
    ExecuteBin = integer_to_list(Execute, 2),
    ReadWriteBin = integer_to_list(ReadWrite, 2),

    {{mode_bin, ModeBin},
     {mode_dec, ModeDec},
     {mode_oct, ModeOct},
     {read, Read, ReadBin, {bool, ((Mode bsr 8) band 1)}, length(ReadBin)},
     {write, Write, WriteBin, {bool, ((Mode bsr 7) band 1)}, length(WriteBin)},
     {execute, Execute, ExecuteBin, {bool, ((Mode bsr 6) band 1)}, length(ExecuteBin)},
     {read_write, ReadWrite, ReadWriteBin, length(ReadWriteBin)}}.