Simple php script to teach myself bitwise operations - also handy utility for calculating Unix/Linux file permissions.

octperm.php

<?php

$input_valid = false;

while ( ! $input_valid ) {

    $input =  readline('Input octal permission string: ');

    if (! preg_match('/[0-7]/', $input))
    {
        echo "Invalid input!\n";
        continue;
    }

    if (mb_strlen($input) > 4)
    {
        echo "Invalid input!\n";
        continue;
    }

    $input_valid = true;
}

$input = octdec($input);

$flags = [
    "special" => [
        's' => 0o4000,
        'g' => 0o2000,
        't' => 0o1000,
    ],
    "owner" => [
        'r' => 0o400,
        'w' => 0o200,
        'x' => 0o100,
    ],
    "group" => [
        'r' => 0o40,
        'w' => 0o20,
        'x' => 0o10,
    ],
    "other" => [
        'r' => 0o4,
        'w' => 0o2,
        'x' => 0o1
    ]
];

$permissions = '';

$special = $flags['special'];

$permissions .= "Special | Owner | Group | Other\n";
$permissions .= "  ";

$permissions .= ($input & $special['s']) ? 's' : '-';   // SUID
$permissions .= ($input & $special['g']) ? 'g' : '-';   // SGID
$permissions .= ($input & $special['t']) ? 't' : '-';   // Sticky
$permissions .= "   |  ";

$owner = $flags['owner'];

$permissions .= ($input & $owner['r']) ? 'r' : '-';
$permissions .= ($input & $owner['w']) ? 'w' : '-';
$permissions .= ($input & $owner['x']) ? 'x' : '-';
$permissions .= "  |  ";

$group = $flags['group'];

$permissions .= ($input & $group['r']) ? 'r' : '-';
$permissions .= ($input & $group['w']) ? 'w' : '-';
$permissions .= ($input & $group['x']) ? 'x' : '-';
$permissions .= "  |  ";

$other = $flags['other'];

$permissions .= ($input & $other['r']) ? 'r' : '-';
$permissions .= ($input & $other['w']) ? 'w' : '-';
$permissions .= ($input & $other['x']) ? 'x' : '-';


echo $permissions . "\n";

I would note there are much better ways to do this, this was just for practice and learning.