How can I get the Unix permission mask from a file? [duplicate]

os.stat is a wrapper around the stat(2) system call interface.

>>> import os>>> from stat import *>>> os.stat("test.txt") # returns 10-tupel, you really want the 0th element ...posix.stat_result(st_mode=33188, st_ino=57197013, \    st_dev=234881026L, st_nlink=1, st_uid=501, st_gid=20, st_size=0, \    st_atime=1300354697, st_mtime=1300354697, st_ctime=1300354697)>>> os.stat("test.txt")[ST_MODE] # this is an int, but we like octal ...33188>>> oct(os.stat("test.txt")[ST_MODE])'0100644'

From here you'll recognize the typical octal permissions.

S_IRWXU 00700   mask for file owner permissionsS_IRUSR 00400   owner has read permissionS_IWUSR 00200   owner has write permissionS_IXUSR 00100   owner has execute permissionS_IRWXG 00070   mask for group permissionsS_IRGRP 00040   group has read permissionS_IWGRP 00020   group has write permissionS_IXGRP 00010   group has execute permissionS_IRWXO 00007   mask for permissions for others (not in group)S_IROTH 00004   others have read permissionS_IWOTH 00002   others have write permissionS_IXOTH 00001   others have execute permission

You are really only interested in the lower bits, so you could chop off the rest:

>>> oct(os.stat("test.txt")[ST_MODE])[-3:]'644'>>> # or better>>> oct(os.stat("test.txt").st_mode & 0o777)

Sidenote: the upper parts determine the filetype, e.g.:

S_IFMT  0170000 bitmask for the file type bitfieldsS_IFSOCK    0140000 socketS_IFLNK 0120000 symbolic linkS_IFREG 0100000 regular fileS_IFBLK 0060000 block deviceS_IFDIR 0040000 directoryS_IFCHR 0020000 character deviceS_IFIFO 0010000 FIFOS_ISUID 0004000 set UID bitS_ISGID 0002000 set-group-ID bit (see below)S_ISVTX 0001000 sticky bit (see below)

I think this is the clearest way of getting a file's the permission bits:

stat.S_IMODE(os.lstat("file").st_mode)

The os.lstat function, will in case the file is a symlink, give you the mode of the link itself, whereas os.stat dereferences the link. Therefore I find os.lstat the most generally useful.

Here's an example case, given regular file "testfile" and symlink to the latter, "testlink":

import statimport osprint oct(stat.S_IMODE(os.lstat("testlink").st_mode))print oct(stat.S_IMODE(os.stat("testlink").st_mode))

This script outputs the following for me:

07770666

Another way to do it if you don't want to work out what stat means is to use the os.access command http://docs.python.org/library/os.html#os.accessBUT read the docs about possible security issues

For instance to check permissions on the file test.dat which has read/write permissions

os.access("test.dat",os.R_OK)>>> True#Execute permissionsos.access("test.dat",os.X_OK)>>> False#And Combinations thereofos.access("test.dat",os.R_OK or os.X_OK)>>> Trueos.access("test.dat",os.R_OK and os.X_OK)>>> False