If you are not cyrstal clear about what permissions are or if you simply don't know how to use them, then John has produced the article for you. John will discuss permissions on the Unix platform and how you can embed permission commands from within a PHP application.
In the past few columns written on www.onlamp.com, I have been discussing using PHP's file I/O capabilities for manipulating both files and directories. This week, we'll take a slight detour from a strictly PHP-related subject and discuss file permissions in Unix systems. If you are using PHP in a Windows environment (or other environment without a permission system), this column may not apply to you.

How Permissions Work

Before we can explain how permissions can be used from within PHP applications, you'll need a little background on how permissions work in general. Although today's column only discusses Unix permission-related commands, these commands directly relate to their PHP counterparts discussed in my next column. If you haven't ever really worked with the permissions system in PHP (or need a refresher) read on.

In a Unix environment, all files and directories are owned by two different entities -- a user and a group. (A group represents multiple individual users.) Likewise, each file in the file system has three different permission sets which determine who can access a particular file or directory. Specifically, every file in a Unix system has the following permission sets: user-level, group-level, and global-level.

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