Convert ls -l output format to chmod format
Some systems have commands to display the permissions of a file as a number, but unfortunately, nothing portable.
zsh
has a stat
(aka zstat
) builtin in the stat
module:
zmodload zsh/stat
stat -H s some-file
Then, the mode
is in $s[mode]
but is the mode, that is type + perms.
If you want the permissions expressed in octal, you need:
perms=$(([##8] s[mode] & 8#7777))
BSDs (including Apple OS/X) have a stat
command as well.
mode=$(stat -f %p some-file)
perm=$(printf %o "$((mode & 07777))"
GNU find (from as far back as 1990 and probably before) can print the permissions as octal:
find some-file -prune -printf '%m\n'
Later (2001, long after zsh
stat
(1997) but before BSD stat
(2002)) a GNU stat
command was introduced with again a different syntax:
stat -c %a some-file
Long before those, IRIX already had a stat
command (already there in IRIX 5.3 in 1994) with another syntax:
stat -qp some-file
Again, when there's no standard command, the best bet for portability is to use perl
:
perl -e 'printf "%o\n", (stat shift)[2]&07777' some-file
You can ask GNU stat
to output the permissions in octal format by using the -c
option. From man stat
:
-c --format=FORMAT use the specified FORMAT instead of the default; output a newline after each use of FORMAT ⋮ %a access rights in octal ⋮ %n file name
So in your case:
bash-4.2$ ls -l foo
-rw-r--r-- 1 manatwork manatwork 0 Apr 7 19:43 foo
bash-4.2$ stat -c '%a' foo
644
Or you can even automate it by formatting stat
's output as valid command:
bash-4.2$ stat -c "chmod %a '%n'" foo
chmod 644 'foo'
bash-4.2$ stat -c "chmod %a '%n'" foo > setpermission.sh
bash-4.2$ chmod a= foo
bash-4.2$ ls -l foo
---------- 1 manatwork manatwork 0 Apr 7 19:43 foo
bash-4.2$ sh setpermission.sh
bash-4.2$ ls -l foo
-rw-r--r-- 1 manatwork manatwork 0 Apr 7 19:43 foo
The above solution will also work for multiple files if using a wildcard:
stat -c "chmod -- %a '%n'" -- *
Will work correctly with file names containing whitespace characters, but will fail on file names containing single quotes.
To convert from the symbolic to octal notation, I once came up with:
chmod_format() {
sed 's/.\(.........\).*/\1/
h;y/rwsxtSTlL-/IIIIIOOOOO/;x;s/..\(.\)..\(.\)..\(.\)/|\1\2\3/
y/sStTlLx-/IIIIIIOO/;G
s/\n\(.*\)/\1;OOO0OOI1OIO2OII3IOO4IOI5IIO6III7/;:k
s/|\(...\)\(.*;.*\1\(.\)\)/\3|\2/;tk
s/^0*\(..*\)|.*/\1/;q'
}
Expanded:
#! /bin/sed -f
s/.\(.........\).*/\1/; # extract permissions and discard the rest
h; # store a copy on the hold space
# Now for the 3 lowest octal digits (rwx), translates the flags to
# binary where O means 0 and I means 1.
# l, L are for mandatory locking (a regular file that has 02000 on
# and not 010 on some systems like Linux). Some ls implementations
# like GNU ls confusingly use S there like for directories even though
# it has nothing to do with setgid in that case. Some ls implementations
# use L, some others l (against POSIX which requires an uppercase
# flag for extra flags when the execution bit is not set).
y/rwsxtSTlL-/IIIIIOOOOO/
x; # swap hold and pattern space, to do a second processing on those flags.
# now only consider the "xXlLsStT" bits:
s/..\(.\)..\(.\)..\(.\)/|\1\2\3/
y/sStTlLx-/IIIIIIOO/; # make up the 4th octal digit as binary like before
G; # append the hold space so we now have all 4 octal digits as binary
# remove the extra newline and append a translation table
s/\n\(.*\)/\1;OOO0OOI1OIO2OII3IOO4IOI5IIO6III7/
:k
# translate the OOO -> 0 ... III -> 7 in a loop
s/|\(...\)\(.*;.*\1\(.\)\)/\3|\2/
tk
# trim leading 0s and our translation table.
s/^0*\(..*\)|.*/\1/;q
That returns the octal number from the output of ls -l
on one file.
$ echo 'drwSr-sr-T' | chmod_format
7654