PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

446 Chapter 19 Interacting with the File System and the Server
The fileowner() and filegroup() functions return the user ID (uid) and group ID
(gid) of the file.These IDs can be converted to names using the functions posix_
getpwuid() and posix_getgrgid(), respectively, which makes them a bit easier to read.
These functions take the uid or gid as a parameter and return an associative array of
information about the user or group, including the name of the user or group, as we
have used in this script.
The fileperms() function returns the permissions on the file.We reformatted them
as an octal number using the decoct() function to put them into a format more familiar
to Unix users.
The filetype() function returns some information about the type of file being
examined.The possible results are fifo, char, dir, block, link, file, and unknown.
The filesize() function returns the size of the file in bytes.
The second set of functions—is_dir(), is_executable(), is_file(), is_link(),
is_readable(), and is_writable()—all test the named attribute of a file and return
true or false.
Alternatively, you could use the function stat() to gather a lot of the same information.When
passed a file, this function returns an array containing similar data to these
functions.The lstat() function is similar, but for use with symbolic links.
All the file status functions are quite expensive to run in terms of time.Their results
are therefore cached. If you want to check some file information before and after a
change, you need to call
clearstatcache();
to clear the previous results. If you want to use the previous script before and after
changing some of the file data, you should begin by calling this function to make sure
the data produced is up to date.
Changing File Properties
In addition to viewing file properties, you can alter them.
Each of the chgrp(file, group), chmod(file, permissions), and chown(file,
user) functions behaves similarly to its Unix equivalent. None of these functions will
work in Windows-based systems, although chown() will execute and always return true.
The chgrp() function changes the group of a file. It can be used to change the group
only to groups of which the user is a member unless the user is root.
The chmod() function changes the permissions on a file.The permissions you pass to
it are in the usual Unix chmod form.You should prefix them with a 0 (a zero) to show
that they are in octal, as in this example:
chmod(‘somefile.txt’, 0777);
The chown() function changes the owner of a file. It can be used only if the script is
running as root, which should never happen, unless you are specifically running the
script from the command line to perform an administrative task.