is_writable

Be warned, that is_writable returns false for non-existent files, although they can be written to the queried path.

In Linux, you might encountering an issue which is a file is not writable even tho it has 644 permission! The problem is with SELinux, just disable it or add rules to allow it.

To Darek and F Dot: About group permissions, there is this note in the php.ini file:
; By default, Safe Mode does a UID compare check when
; opening files. If you want to relax this to a GID compare,
; then turn on safe_mode_gid.
safe_mode_gid = Off

Check director is writable recursively. to return true, all of directory contents  must be writable

<?php
function is_writable_r($dir) {
    if (is_dir($dir)) {
        if(is_writable($dir)){
            $objects = scandir($dir);
            foreach ($objects as $object) {
                if ($object != "." && $object != "..") {
                    if (!is_writable_r($dir."/".$object)) return false;
                    else continue;
                }
            }    
            return true;    
        }else{
            return false;
        }
        
    }else if(file_exists($dir)){
        return (is_writable($dir));
        
    }
}

?>

It appears that is_writable() does not check full permissions of a file to determine whether the current user can write to it.  For example, with Apache running as user 'www', and a member of the group 'wheel', is_writable() returns false on a file like

-rwxrwxr-x           root         wheel          /etc/some.file

Regarding you might recognize your files on your web contructed by your PHP-scripts are grouped as NOBODY you can avoid this problem by setting up an FTP-Connection ("ftp_connect", "ftp_raw", etc.) and use methods like "ftp_fput" to create these [instead of giving out rights so you can use the usual "unsecure" way]. This will give the files created not the GROUP NOBODY - it will give out the GROUP your FTP-Connection via your FTP-Program uses, too.

Furthermore you might want to hash the password for the FTP-Connection - then check out:
http://dev.mysql.com/doc/mysql/en/Password_hashing.html

This file_write() function will give $filename the write permission before writing $content to it.

Note that many servers do not allow file permissions to be changed by the PHP user.

<?php
    function file_write($filename, &$content) { 
        if (!is_writable($filename)) {
            if (!chmod($filename, 0666)) {
                 echo "Cannot change the mode of file ($filename)";
                 exit;
            };
        }
        if (!$fp = @fopen($filename, "w")) {
            echo "Cannot open file ($filename)";
            exit;
        }
        if (fwrite($fp, $content) === FALSE) {
            echo "Cannot write to file ($filename)";
            exit;
        } 
        if (!fclose($fp)) {
            echo "Cannot close file ($filename)";
            exit;
        }
    } 
?>

The results of this function seems to be not cached :
Tested on linux and windows

<?php
chmod($s_pathFichier, 0400);
echo'<pre>';var_dump(is_writable($s_pathFichier));echo'</pre>';
chmod($s_pathFichier, 04600);
echo'<pre>';var_dump(is_writable($s_pathFichier));echo'</pre>';
exit;
?>

This function returns always false on windows, when you check an network drive.

See PHP Bug https://bugs.php.net/bug.php?id=68926
See https://stackoverflow.com/q/54904676

Do note that is_readable/is_writable evaluates permissions in an attempt to produce the result.

This WILL fail in certain situations, while the file is actually accessible to the user, but manual evaluation fails to connect the dots.

The only trusted way to detect if a file is readable is to actually open it for reading. The only trusted way to detect if a file is writable is to actually open it for writing. And catch the error in case of failure.

I've encountered an unexpected issue: even though the directory allows writing files, it keeps returning false.

```
$a = 'C:/Users/*/OneDrive/work/www/';
$b = "{$a}admin/";
var_dump($a);
var_dump(is_writable($a));
var_dump($b);
var_dump(is_dir($b));
var_dump(is_writable($b));
var_dump(file_put_contents($b.'test.txt','hello'));
```

- string 'C:/Users/*/OneDrive/work/www/' (length=33)
- boolean true
- string 'C:/Users/*/OneDrive/work/www/admin/' (length=39)
- boolean true
- boolean false
- int 5