Extended attributes make it possible to store (additional) file metadata on a per-file basis. This can, for example, be used to save & restore file permissions.

mkdir -p ~/Desktop/testdir
touch ~/Desktop/testdir/f{1,2,3}.txt
find -x ~/Desktop/testdir -print0 | xargs -0 stat -LF
stat -x ~/Desktop/testdir/f1.txt

which xattr   # /opt/local/bin/xattr; sudo port install xattr (after installing MacPorts, http://www.macports.org/install.php)


# store file permissions as additional Unix file metadata with xattr

find -x ~/Desktop/testdir -print0 | while read -d $'\0' filename; do
#find -x ~/Desktop/testdir -type f -or -type d -print0 | while read -d $'\0' filename; do
   fchmod="$(stat -f %p "$filename")"; \
   fchown="$(stat -f %u:%g "$filename")"; \
   xattr --set fchmod "$fchmod" "$filename"; \
   xattr --set fchown "$fchown" "$filename"; \
   #echo $fchown $fchmod; \
done


find -x ~/Desktop/testdir -print0 | xargs -0 xattr --list
find -x ~/Desktop/testdir -print0 | xargs -0 stat -LF

# change file permissions & ownership
sudo chown -R root:wheel ~/Desktop/testdir
sudo chmod -R 700 ~/Desktop/testdir

sudo find -x ~/Desktop/testdir -print0 | xargs -0 sudo stat -LF
find -x ~/Desktop/testdir -print0 | xargs -0 xattr --list
sudo find -x ~/Desktop/testdir -print0 | xargs -0 sudo xattr --list


# restore file permissions & ownership

sudo find -x ~/Desktop/testdir -print0 | while read -d $'\0' filename; do 
   fchown="$(sudo xattr --get fchown "$filename" | awk '/fchown/ {print $2}')"; \
   fchmod="$(sudo xattr --get fchmod "$filename" | awk '/fchmod/ {print $2}')"; \
   sudo chown "$fchown" "$filename"; \
   sudo chmod "$fchmod" "$filename"; \
   #echo $fchown $fchmod; \
done


find -x ~/Desktop/testdir -print0 | xargs -0 stat -LF
find -x ~/Desktop/testdir -print0 | xargs -0 xattr --list

# convert from octal to symbolic format

function o2s () { touch ~/.octal2symbolic; chmod -vv "$@" $_;  ls -l $_ | awk '{print $1}'; rm -f ~/.octal2symbolic; }
#function o2s () { touch ~/.octal2symbolic; chmod "$@" $_;  ls -l $_ | awk '{print $1}'; rm -f ~/.octal2symbolic; }

o2s 755
o2s 644
o2s 1744
o2s 0100751      # cf. man 2 stat (st_mode)
o2s 0101751


# Cf. Bash 'umask' builtin doesn't set 'x' permissions?
# http://archives.devshed.com/forums/unix-linux-135/bash-umask-builtin-doesn-t-set-x-permissions-372356.html

UMASKO=$(umask)   # 0022

help umask
umask
umask -p
umask -S

umask 0077
umask
umask -S
o2s 755

umask 0000
umask
umask -S
o2s 654

umask $UMASKO



# convert from symbolic to octal format
# default file permissions of temporary file: chmod 777 ~/.symbolic2octal

function s2o () { touch ~/.symbolic2octal; chmod 777 $_; chmod "$@" $_;  stat -f %p $_; rm -f ~/.symbolic2octal; }

s2o a-x
s2o u=rwx,g=rx,o=x
s2o u=rwx,g=rx,o=x,+t