I'll begin with something simple - opening a file and reading its contents. Let's assume that we have a text file called "mindspace.txt", containing the following random thoughts:

  We're running out of space on planet Earth. 

  Scientists are attempting to colonize Mars. 

  I have a huge amount of empty real estate in my mind. 

  Imagine if I could rent it to the citizens of Earth for a nominal monthly fee. 
  

  Would I be rich? Or just crazy?

  

Now, in order to read this data into a PHP script, I need to open this file and assign it a file handle - I can then use this file handle to interact with the file and extract its contents into a PHP variable. Take a look:

  <?php

// set file to read

  $filename = "mindspace.txt";
// open file

  $fh = fopen($filename, "r") or die("Could not open file!");
// read file contents

  $data = fread($fh, filesize($filename)) or die("Could not read file!");
// close file

  fclose($fh);
// print file contents

  echo $data . " -- ALL DONE --";
?>

  

And when you run this script, PHP should return the contents of the file "mindspace.txt", with a message at the end.

A quick explanation: in order to read data from an external file, PHP requires you to define a file handle for it with the fopen() function. I've done this in the very first line of the script above.

  <?php

// set file to read

  $filename = "mindspace.txt";
// open file

  $fh = fopen($filename, "r") or die("Could not open file!");
?>

  

You can specify a full path to the file as well:

  <?php

// set file to read

  $filename = "/home/me/mindspace.txt";
// open file

  $fh = fopen($filename, "r") or die("Could not open file!");
?>

  

Notice the second argument to fopen() - it's a string indicating the "mode" in which the file is to be opened. A number of modes are available - read, write, append and so on - and I'll discuss them in detail a little further along.

If the fopen() function is successful, it returns a file handle (stored in
$fh) which can be used for further interaction with the file. This file handle is provided to the fread() function, which uses it to read the contents of the file.

  <?php

// read file contents

  $data = fread($fh, filesize($filename)) or die("Could not read file!");
?>

  

The second argument to fread() is the number of bytes to be read. In this case, I've used the filesize() function to obtain the size of the file in bytes and provide that number to the fread() function; you can set an arbitrary value here if you like, but be warned that reading will automatically stop once the end of the file is reached.

Once the file contents have been read into a variable with fread(), the
fclose() function is used to close the file and destroy the file handle created by fopen(). This is not strictly necessary, but it is a good habit to develop as it avoids loose ends cluttering up your script.

  <?php

// close file

  fclose($fh);
?>