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is_writable

(PHP 4, PHP 5)

is_writableIndica si un archivo existe y es escribible

Descripción

bool is_writable ( string $filename )

Devuelve TRUE si filename existe y es escribible. El argumento nombre_archivo puede ser el nombre de un directorio, permitiendo así comprobar si el directorio es escribible.

Tenga en cuenta que PHP puede estar accediendo al archivo bajo el id de ususario por el que se está ejecutando el servidor web (a menudo 'nobody'). Las limitaciones del modo seguro no se toman en cuenta.

Parámetros

filename

El nombre de archivo que va a ser comprobado.

Valores devueltos

Devuelve TRUE si el parámetro filename existe y es escribible.

Ejemplos

Ejemplo #1 Ejemplo de is_writable()

<?php
$nombre_archivo 
'prueba.txt';
if (
is_writable($nombre_archivo)) {
    echo 
'El archivo es escribible';
} else {
    echo 
'El archivo no es escribible';
}
?>

Errores/Excepciones

En caso de fallo, se emite un E_WARNING.

Notas

Nota: Los resultados de esta función son guardados en caché. Para más información ver clearstatcache().

Sugerencia

Desde PHP 5.0.0, esta función también puede usarse con algunos URL wrappers. Consultar Protocolos y Envolturas soportados para deter4minar qué envolturas soportan la familia de funcionalidad de stat().

Ver también

  • is_readable() - Indica si un fichero existe y es legible
  • file_exists() - Comprueba si existe un fichero o directorio
  • fwrite() - Escritura de un archivo en modo binario seguro

add a note add a note

User Contributed Notes 11 notes

up
7
darek at fauxaddress dot com
8 years ago
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
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4
starrychloe at yahoo dot com
6 years ago
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
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2
gr
3 years ago
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;
?>
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1
agrenier at assertex dot com
10 years ago
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;
        }
    }
?>
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2
JimmyNighthawk
9 years ago
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
up
1
greg at gregwhitescarver dotcalm
8 years ago
In response to Darek:

We have two servers: one running PHP 5.0.4 and Apache 1.3.33, the other running PHP 4.3.5 and Apache 1.3.27.  The PHP 4 server exhibits the behavior you are describing, with is_writable() returning 'false' even though the www user is in the group that owns the file, but the PHP 5 server is returning 'true.'
up
0
samuel dot zallocco at univaq dot it
1 month ago
Check if a directory is writable. Work also on mounted SMB shares:

function isWritablePath($home, $xpath) {
    $isOK = false;
    $path = trim($xpath);
    if ( ($path!="") && (strpos($path,$home)!==false)  && is_dir($path) && is_writable($path) ) {
        $tmpfile = "mPC_".uniqid(mt_rand()).'.writable';
        $fullpathname = str_replace('//','/',$path."/".$tmpfile);
        $fp = @fopen($fullpathname,"w");
        if ($fp !== false) {
            $isOK = true;
        }
        @fclose($fp);
        @unlink($fullpathname);
    }
    return $isOK;
   
}
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0
yury dot gugnin at gmail dot com
6 months ago
function is_writable('ftp://user.....') always return false. I can create/delete files, but can check is writable. Is this bug or php feature :)?
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0
legolas558 d0t users dot sf dot net
7 years ago
This is the latest version of is__writable() I could come up with.
It can accept files or folders, but folders should end with a trailing slash! The function attempts to actually write a file, so it will correctly return true when a file/folder can be written to when the user has ACL write access to it.

<?php
function is__writable($path) {
//will work in despite of Windows ACLs bug
//NOTE: use a trailing slash for folders!!!
//see http://bugs.php.net/bug.php?id=27609
//see http://bugs.php.net/bug.php?id=30931

   
if ($path{strlen($path)-1}=='/') // recursively return a temporary file path
       
return is__writable($path.uniqid(mt_rand()).'.tmp');
    else if (
is_dir($path))
        return
is__writable($path.'/'.uniqid(mt_rand()).'.tmp');
   
// check tmp file for read/write capabilities
   
$rm = file_exists($path);
   
$f = @fopen($path, 'a');
    if (
$f===false)
        return
false;
   
fclose($f);
    if (!
$rm)
       
unlink($path);
    return
true;
}
?>
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0
legolas558 dot sourceforge comma net
8 years ago
Since looks like the Windows ACLs bug "wont fix" (see http://bugs.php.net/bug.php?id=27609) I propose this alternative function:

<?php

function is__writable($path) {

if (
$path{strlen($path)-1}=='/')
    return
is__writable($path.uniqid(mt_rand()).'.tmp');

if (
file_exists($path)) {
    if (!(
$f = @fopen($path, 'r+')))
        return
false;
   
fclose($f);
    return
true;
}

if (!(
$f = @fopen($path, 'w')))
    return
false;
fclose($f);
unlink($path);
return
true;
}

?>

It should work both on *nix and Windows

NOTE: you must use a trailing slash to identify a directory
up
0
claude dot paroz at ne dot ch
10 years ago
Under Windows, it only returns the read-only attribute status, not the actual permissions (ACL).
See http://bugs.php.net/bug.php?id=27609
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