The permissions of a file in a Linux system are split into three sets of three permissions: read, write, and execute for the owner, group, and others. Each of the three values can be expressed as an octal number summing each permission, with 4 correspondings to read, 2 to write, and 1 to execute. Or it can be written with a string using the letters r, w, and x or - when the permission is not granted.

For example, 640 is read/write for the owner, read for the group, and no permissions for the others; converted to a string, it would be: "rw-r-----"

Similarly, 755 is read/write/execute for the owner, and read/execute for group and others; converted to a string, it would be: "rwxr-xr-x"

Summary:

Python Code to convert from octal to string representation of Linux file permissions:

def octal_to_string(octal):
    result = ""
    value_letters = [(4,"r"),(2,"w"),(1,"x")]
    # Iterate over each of the digits in octal
    for digit in [int(n) for n in str(octal)]:
        # Check for each of the permissions values
        for value, letter in value_letters:
            if digit >= value:
                result += letter
                digit -= value
            else:
                result += '-'
    return result
    
print(octal_to_string(755)) # Should be rwxr-xr-x
print(octal_to_string(644)) # Should be rw-r--r--
print(octal_to_string(750)) # Should be rwxr-x---
print(octal_to_string(600)) # Should be rw-------

Output:

When executed the program will print below output.

rana@brahma:Python-Scripts$ python3 permission.py 
rwxr-xr-x
rw-r--r--
rwxr-x---
rw-------

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