File Handling in PHP

by Jeff Wheeler aka nokrev   | filed under PHP and MySQL

When writing applications for the web, it's often important to be able to save data. This is usually done one of two ways: writing data to a file, or saving it in a database (such as MySQL). Of course, the easier method (which doesn't require other technologies) is to write to files, and then read and parse them yourself. This simpler which is what I discuss here.

So, let's get started:

1. To open a file for reading and writing, we start by using the fopen function. This simply opens up a file resource for us to use in later functions.
   
   <?php $filename = 'file.txt'; $handle = fopen($filename, 'r'); ?>
   
   It's worth noting that I opened the file for reading. Notice the 'r'? This is the mode argument, and allows you to use the $file variable for reading, or writing, depending on which you need.
   
   You can see the different modes for opening a file in the documentation for the function (under Table 1).
2. To read from a file, the easiest way is to utilize the fread method. This takes two arguments, the file resource from the previous function (fopen), and a length argument.
   
   <?php $content = fread($handle, filesize($filename)); ?>
   
   I had to use filesize in order to read to the end of the file. Otherwise, the function won't know when to stop reading.
3. Writing to a file is done with similar ease. This time, we'll just use fwrite, which has two required arguments: the file handle resource, and the string to write (the third optional argument is the length of the content to write).
   
   <?php $handle = fopen($filename, 'a'); fwrite($handle, 'Hello World!'); ?>
   
   I had to redefine the $handle variable, because the previous resource was only open for reading.

The Shortcuts

Well, since you know how to open, read, and write files the full, long way, here are some shortcuts. I tend to avoid these, but there's really nothing wrong with using them. Please be aware, both of these require PHP5.

1. Rather than fopen and fread, you can simply use file_get_contents. The only required argument is the filename, and it'll return a string of the contents.
   
   <?php $contents = file_get_contents('file.txt'); ?>
2. Now, the shortcut for fwrite is just as simple…
   
   <?php file_put_contents('file.txt', 'Hello World!'); ?>

In the next section, I will cover how to list files in directories and more!

In the previous section, you got an introduction to using PHP to manipulate files. In this page, we will pick up from where we left off and discuss how to list files from a directory.

Listing Files

Occasionally, it's nice to use PHP to list all files in a certain directory. This can be achieved via the dir class.

1. First, we have to initiate the dir object with the directory we want to look through. If it's the current directory, use '.', as this references the current directory.
   
   <?php $dir = dir('.'); ?>
2. The next part is a little bit more complicated, but that is because the PHP documentation recommends a complex but short way to do what we intended.
   
   I use the while control structure, to loop through all the entries. For the condition, I test if the $dir->read() returns false (the !== operator tests for the correct type, so '' would not evaluate to 0 or false, as it would with a non-type-sensitive operator). I also define $file inside the expression, but the assignment will return the final value of $file after the assignment. The $dir->read() method will return false in the case that there are no more files, and it'll break out of the loop.
   
   <?php while (false !== ($file = $dir->read())) { echo $file."\n"; } ?>
   
   If you are using html, you will want to use a <br /> instead of a newline character, so that the files will appear on new lines in your page.
3. If you executed the previous code, you will notice two strange files listed in your script's output: . and ... These are references to the current directory (the '.'), and the parent directory (the '..').
   
   If you want to exclude these from your list, simply write an if statement that tests whether the $file variable is either of those values, and if so, ignore it.
   
   <?php while (false !== ($file = $dir->read())) { if ($file != '.' && $file != '..') { echo $file."\n"; } } ?>
4. It's necessary to close instances of the dir class when you're done with them, in order to clean the resource handle, and announce to the operating system that you're done with it.
   
   <?php $dir->close(); ?>

This wraps up learning how to list files using PHP. In the next section, you will learn how to upload files from a directory to the server. Before I send you off to the next section though, for another practical use of being able to retrieve a list of files from a directory, read Kirupa's tutorial on Parsing External Data.

More file handling coverage in the next section!

Yay, this is the previous section! In the previous section you learned more practical file handling tricks, and we will wrap things up on this page.

Uploading Files

Allowing users to upload files is a necessity of many sites, so, how does one do that, exactly? Turns out, there's some handy documentation written on that. Having trouble getting all that? Well, here's some help that's slightly easier to digest.

1. First, you'll need an html page where the form will lie. This form must define the max file-size for the upload, and must have the file upload field itself.
   
   <form enctype="multipart/form-data" action="upload.php" method="POST"> <input type="hidden" name="MAX_FILE_SIZE" value="30000" /> <input name="userfile" type="file" /> <input type="submit" value="Send File" /> </form>
   
   The MAX_FILE_SIZE defines the largest possible file-size, in bytes, of course. The name attribute of the upload field (designated by the file value for the type attribute) is the important part, as we will later use this in our script to know which file to upload (this is used to support multiple uploads).
2. Next, we have to upload the file. But first, it's important to understand the $_FILE[] array.
   
   In the $_FILE[] array, there's one entry for each upload field in the form which sent the user to this script. So, in our case, there is one index named 'userfield', for the one field with that name in our form. Each value in the array is also an associative array, with the following keys and values (reworded for clarity from documentation):

Table 1: A summary of the keys and values

3. So, now we can get down to business. We start by getting the filename we will want to give the uploaded file, and the directory where we will want to put it.
   
   <?php $target_file = '/path/to/upload/'.basename($_FILES['userfile']['name']); ?>
   
   The use of basename is absolutely necessary. Without this, you're running a huge security risk. If a user were to upload a file with a name that started with a relative path going up, such as ../../../, they would eventually get to root, and could navigate to anywhere on the filesystem by putting in more directories after the original starting path.
   
   

   Warning:

   It is very important that you make sure the server has permissions to write to this directory. If your server is running any distro of Linux or Mac OS X, you'll likely need to chmod the directory.
4. Next, you simply need to move the uploaded file to $target_file. I suggest doing this in an if, in order to test for success.
   
   <?php if (move_uploaded_file($_FILES['userfile']['tmp_name'], $target_file)) { // Succeeded echo 'Yay!'; } else { // Failed echo 'No!'; } ?>

That's really all there is to it. Pretty simple, huh? You can expand on this, by reading PHP's documentation on serializing and unserializing objects. If you have any questions, feel free to post them on the forums.
 

Jeff Wheeler Nokrev.com

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