Shell Programming and Scripting

perl -le'printf "%o", 07777 & (stat)[2] for @ARGV' <file>

ls -l file | awk '{split ($1, X, ""); for (i=2; i<=10; i++) PERM+=2^(10-i)*(X[i]=="-"?0:1) ; printf "%o\n", PERM}'
644

ls -l file | 
awk     '{split ($1, X, "")             # split the mode in $1 into single chars
          for (i=2; i<=10; i++)         # run across 9 chars starting from 2
                 PERM+=2^(10-i)*        # sum binary weight of position times
                        (X[i]=="-"?0:1) # 0 if char is a dash else 1
          printf "%o\n", PERM}'         # print octal value

mode="-rwxr-x---"
v=${mode#?}
v=${v//-/0}
v=${v//[rwx]/1}
printf "%03o\n" $((2#$v))

750

#!/bin/sh
mode="-rwsr-x--x"
spec=$(echo $mode | sed 's/^...\(.\)..\(.\)..\(.\)/\1\2\3/')
spec=${spec//[x-]/0}
spec=${spec//[sStT]/1}
v=${mode#?}
v=${v//[-ST]/0}
v=${v//[rwxst]/1}
if [ $spec -gt 0 ]
then
   printf "%o%03o\n" $((2#$spec)) $((2#$v))
else
    printf "%03o\n" $((2#$v))
fi

4751