Page 336 - Beginning PHP 5.3

Part III: Using PHP in Practice
Understanding Files and Directories

Everything on your hard drive is stored as a file of one kind or another, although most folks think in
terms of files and directories. There are ordinary program files, data files, files that are directories, and
special files that help the hard drive keep track of the contents of folders and files. PHP has functions
that can work with any file type, but typically you ’ ll be working with text files that contain data.

The terms “ directory ” and “ folder ” are used interchangeably in this book (and in the PHP community);
they mean exactly the same thing.

A file is nothing more than an ordered sequence of bytes stored on a hard disk or other storage media.
A directory is a special type of file that holds the names of the files and directories inside the folder
(sometimes denoted as subdirectories or subfolders ) and pointers to their storage areas on the media.

Many differences exist between UNIX - based and Windows operating systems, one of them being the
way directory paths are specified. UNIX - based systems such as Linux use slashes to delimit elements in
a path, like this:
/home/matt/data/data.txt

Windows uses backslashes:

C:\MyDocs\data\data.txt
Fortunately, PHP on Windows automatically converts the former to the latter in most situations, so you
can safely use slashes in your script, regardless of the operating system that the script is running on.
Occasionally, though, backslashes are necessary. In this situation, you need to use two backslashes in a
row, because PHP interprets a backslash as escaping the following character:

“C:\\MyDocs\\data\\data.txt”

Getting Information on Files

PHP provides some functions that enable you to access useful file information. For example, you can use
file_exists() to discover whether a file exists before attempting to open it:

file_exists( “/home/chris/myfile.txt” )

file_exists() returns true if the file at the specified path exists, or false otherwise.

In a similar fashion, you can use the filesize() function to determine the size of a file on the hard
disk. Just as with file_exists() , this function takes a filename as an argument:

filesize( “/home/chris/myfile.txt” )

This returns the size of the specified file in bytes, or false upon error.

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