PHP File Permissions

PHP File Permissions

Summary: in this tutorial, you will learn how to deal with PHP file permissions including checking and changing file permissions.

File permissions specify what you can do with a particular file in the system e.g., reading, writing or executing the file. Notice that PHP automatically grants appropriate permissions behind the scenes. For example, if you creates a new file for writing, PHP automatically grants read and write permissions to you.

In addition, PHP also provides some useful functions for checking and changing the file permissions.

PHP checking file permissions

PHP gives you three handy functions that allow you to check file permissions:

• is_readable() returns true if you are allowed to read the file, otherwise returns false.
• is_writable() returns true if you are allowed to write the file, otherwise returns false.
• is_executable() returns true if you are allowed to execute the file, otherwise returns false.

Let’s take a look at the following example:

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<?php $fn = './test.text';   $msg = is_readable($fn) ? $msg = 'File is readable' : $msg = 'File is not readable'; echo $msg . '<br/>';   $msg = is_writable($fn) ? $msg = 'File is writable' : $msg = 'File is not writable';   echo $msg . '<br/>';   $msg = is_executable($fn) ? $msg = 'File is executable'   : $msg = 'File is not executable';   echo $msg . '<br/>';

Besides those functions, PHP also provides the fileperms() function that returns an integer, which represents the permissions that are set on a particular file.

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<?php $fn = './test.txt'; $fp = fileperms($fn);   echo substr(sprintf('%o', $fp), -4); //0666

PHP changing file permissions

To change the file permissions, or mode, you use chmod() function. First, you need to pass the name of the file that you want to set permission. Second, you need to specify the desired permission. The chmod() function returns true if the permission was set successfully otherwise it returns false.

A file permission is represented by an octal number that contains three digits:

• The first digit specifies what the owner of the file can do with file.
• The second digit specifies what the owner group of the file can do with the file.
• The third digit specifies what everyone can do with the file.

The following table illustrates the value of each digit that represents the access permission for particular users ( user, user group or everyone) :

Value	Permission
0	cannot read, write or execute
1	can only execute
2	can only write
3	can write and execute
4	can only read
5	can read and execute
6	can read and write
7	can read, write and execute

For example, to set a permission that only creator or owner can read and write a file, everyone else only can read the file, we use the following code:

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<?php $fn = './test.txt'; chmod($fn, 0644);

Notice that we put 0 before 644 to ask PHP to interpret it as an octal number.