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

Thanks for writing and posting this! This was very helpful in writing my own parser. If you need to convert from symbolic to numeric you can use this function.

def perm_to_num(symbolic):
    '''
    Convert symbolic permission notation to numeric notation.
    '''
    perms = {
            '---': '0',
            '--x': '1',
            '-w-': '2',
            '-wx': '3',
            'r--': '4',
            'r-x': '5',
            'rw-': '6',
            'rwx': '7'
        }

    # Trim Lead If It Exists
    if len(symbolic) == 10:
        symbolic = symbolic[1:]

    # Parse Symbolic to Numeric
    x = (symbolic[:-6], symbolic[3:-3], symbolic[6:])
    numeric = perms[x[0]] + perms[x[1]] + perms[x[2]]
    return numeric

This will convert input like '-rw-r--r--' to '644'

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'