Linux Tips and Tricks

Retrieve File Permission In Octal Representation – Shell Scripting

June25

In most of the linux flavors, you will be having a command called ‘stat’

Using the stat command, we can easily retrieve the permission of a file in octal representation

1	stat -c '%a' filename.txt

Octal digit	Text equivalent	Binary value	Meaning
0	`---`	000	All types of access are denied
1	`--x`	001	Execute access is allowed only
2	`-w-`	010	Write access is allowed only
3	`-wx`	011	Write and execute access are allowed
4	`r--`	100	Read access is allowed only
5	`r-x`	101	Read and execute access are allowed
6	`rw-`	110	Read and write access are allowed
7	`rwx`	111	Everything is allowed

we can write a awk function to calculate the permission in octal representation

$cat permission.awk
function cal(str)
{
    a=0;
    if(str~/r/)
    {
        a+=4;
    }
    if(str~/w/)
    {
        a+=2;
    }
    if(str~/x/)
    {
        a+=1;
    }
}
{
for(i=2;<=length($1);i=i+3)
{
	cal(substr($1,i,3))
	octal=octal""a;
}
print octal
}

$ chmod 000 a.txt 
$ ls -l a.txt | awk -f permission.awk 
000 
 
$ chmod 001 a.txt 
$ ls -l a.txt | awk -f permission.awk 
001 
 
$ chmod 031 a.txt 
$ ls -l a.txt | awk -f permission.awk 
031

One more function from ctsgnb

#!/bin/bash
 
function conv_perm(){
  binary1=`echo "$1" | cut -c4,7,10|tr xstST- 011110`
  binary2=`echo "$1" | cut -c2-10 | tr rwsxtST- 11111000`
  octal=`echo "obase=8;ibase=2;${binary1}${binary2}"|bc`
  echo "$octal"
}
 
#Call the function
conv_perm "-rwxrwxrwx"
conv_perm "-r-x-wx-wx"
conv_perm "-r-x--x-w-"