Python script to convert a Linux octal permission number to a text string

perm_to_text.py

def perm_to_text(perm):
    perms = {
        "0": "---",
        "1": "--x",
        "2": "-w-",
        "3": "-wx",
        "4": "r--",
        "5": "r-x",
        "6": "rw-",
        "7": "rwx"
        }
    if len(perm) == 4:
        first = perm[0]
        perm = perm[1:]
    else:
        first = ""

    try:
        outperms = ""
        for p in perm:
            outperms += perms[p]
    except KeyError as e:
        outperms = perm

    if first != "":
        if first == '0':
            pass
        elif first == '1':
            pass
        elif first == '2':
            if outperms[5] == 'x':
                outperms = outperms[:5]+'s'+outperms[6:]
            else:
                outperms = outperms[:5]+'S'+outperms[6:]
        elif first == '4':
            if outperms[2] == 'x':
                outperms = outperms[:2]+'s'+outperms[3:]
            else:
                outperms = outperms[:2]+'S'+outperms[3:]
        else:
            outperms = perm

    return "-"+outperms

Sorry, my function does exactly the reverse of the initial question... It's like the post from Justin Timperio

I have a version which handles the additional permissions like Sticky bit, Set User/Group bits. For instance, it converts 'rwsr-Sr-T'. Note that my code is extracted from my tools and allows to pass an octal value (usually a mistake). Here is the code 👍

def set_fmode(value) :
    """
    Convert a 'rwsr-xr-T' format to a decimal value
    """

    lvalue = len(value)

    # Check if 'value' has the right format
    if (isinstance(value,
                   str)
        and not [x for x in value if x not in '-rwxXsStT']
        and lvalue == 9) :

        pos = lvalue - 1
        res = 0
        for c in value :
            if c in 'sStT' :
                # Special modes
                res += (1 << pos // 3) << 9

            res += 1 << pos if c in 'rwxst' else 0
            pos -= 1

    elif isinstance(value,
                    int) :
        res = value

    else :
        raise ValueError
    
    return res

import stat
stat.filemode(0o107664) # '-rwSrwSr-T'