PHP 101 (part 5): Rank and File

Back to School
Handle With Care
•  Open the file and assign it a file handle
•  Interact with the file via its handle and extract its contents into a PHP variable
•  Close the file
Different Strokes

When Laziness is a Virtue
Writing to Ma
Information is Power
Breaking Eggs



Back to School

When you first started reading this series, I promised you that
you’d have a whole lot of fun. If you’re the cynical type, you may be
feeling that I didn’t keep my promise. After all, how much fun have you
really had so far? All you’ve done is learn a bunch of
theoretical rules, added and subtracted numbers from each other, learnt
primitive decision-making and gone round and round in the circular
funhouse of loops. Heck, if this wasn’t a PHP tutorial, it would be
kindergarten…

I hear you.

In this segment of our ongoing saga, I’m going to teach you how to
do something that’s definitely not for kids. It involves getting down
and dirty with files on the disk: meeting them (shock!), reading their
contents (shriek!) and (horror of horrors!) writing data to them. All
of these exciting activities will take place under the aegis of PHP’s
very cool file manipulation API, which allows you to view and modify
file attributes, read and list directory contents, alter file
permissions, retrieve file contents into a variety of native data
structures, and search for files based on specific patterns.

Let’s get started!


Handle With Care

I’ll begin with something simple: opening a file and reading its
contents. Let’s assume that somewhere on your disk, hidden under
/usr/local/stuff/that/should/be/elsewhere/recipes/, you have a text
file containing the recipe for the perfect Spanish omelette. You now wish
to read the contents of this file into a PHP script.

In order to do this, there are three distinct steps to be
followed:

  • Open the file and assign it a file handle.
  • Interact with the file, via its handle, and extract its contents
    into a PHP variable.
  • Close the file.

Here’s a PHP script that does just that:



<?php

// set file to read
$file = '/usr/local/stuff/that/should/be/elsewhere/recipes/omelette.txt' or die('Could not open file!');

// open file

$fh = fopen($file, 'r') or die('Could not open file!');

// read file contents

$data = fread($fh, filesize($file)) or die('Could not read file!');

// close file

fclose($fh);

// print file contents

echo $data;

?>



Run this script through your Web browser, and PHP should return the
contents of the file.

Now let me explain each of the three steps above in detail:


Open the file and assign it a file handle

PHP needs a file handle to read data from a file. This file handle
can be created with the fopen() function, which accepts two arguments:
the name and path to the file, and a string indicating the “mode” in
which the file is to be opened ('r' for read).

Three different modes are available for use with the fopen()
function. Here’s the list:

'r' – opens a file in read mode

'w' – opens a file in write mode, destroying existing file
contents

'a' – opens a file in append mode, preserving existing file
contents


Interact with the file via its handle and extract its contents
into a PHP variable

If the fopen() function is successful, it returns a file handle,
$fh, which can be used for further interaction with the file. This file
handle is used by the fread() function, which reads the file and places
its contents into a variable.

The second argument to fread() is the number of bytes to be read.
You can usually obtain this information through the filesize()

function, which – who’d have guessed it?!- returns the size of the
file in bytes.


Close the file

This last step is not strictly necessary as PHP closes the file
automatically once it reaches the end of the script, but it’s a good
habit to develop. Explicitly closing the file with fclose() has two
advantages: it ties up loose ends in your script, and it wins you lots
of good karma from the PHP community.

You probably haven’t see the die() function before, either. This
function is mostly used as a primitive error-handling mechanism. In the
event of a fatal error, such as the file path being invalid or the file
permissions being such that PHP cannot read it, die() terminates script
processing and optionally displays a user-specified error message
indicating why it committed suicide.


Different Strokes

An alternative method of reading data from a file is the very cool
file() function, which reads the entire file into an array (remember
them?) with one line of code. Each element of the array then contains
one line from the file. To display the contents of the file, simply
iterate over the array in a foreach() loop and print each element.

The following example demonstrates:

<?php

// set file to read
$file = '/usr/local/stuff/that/should/be/elsewhere/recipes/omelette.txt' or die('Could not read file!');

// read file into array

$data = file($file) or die('Could not read file!');

// loop through array and print each line

foreach ($data as $line) {

     echo
$line;

}

?>



In this example, the file() command opens the file, reads it into an
array and closes the file – all in one, single, elegant movement. Each
element of the array now corresponds to a line from the file. It’s easy
to print the file’s contents now – just reach for that mainstay of
array processing, the foreach() loop.

Don’t want the data in an array? Try the file_get_contents()
function, new in PHP 4.3.0 and PHP 5.0, which reads the entire file
into a string:



<?php

// set file to read
$file = '/usr/local/stuff/that/should/be/elsewhere/recipes/omelette.txt' ;

// read file into string

$data = file_get_contents($file) or die('Could not read file!');

// print contents

echo $data;

?>



Who am I kidding? I always use the one-line functions noted above
instead of the three-line sequence of fopen(), fread() and fclose().
Laziness conquers all.


When Laziness is a Virtue

PHP also offers two very useful functions to import files into a PHP
script: the include() and require()functions. These functions can be
used to suck external files lock, stock and barrel into a PHP script,
which is very handy if, for example, you have a modular application
which has its code broken down across files in separate locations.

The best way to understand the utility of the include() and
require() functions is with an example. Assume that on your Web site
you have a standard menu bar at the top of every page, and a standard
copyright notice in the bottom. Instead of copying and pasting the
header and footer code on each individual page, PHP gurus simply create
separate files for the header and footer, and import them at the top
and bottom of each script. This also makes a change to the site design
easier to implement: instead of manually editing a gazillion files, you
simply edit two, and the changes are reflected across your entire site
instantaneously.

Let’s see a real live example of this in action. Create the header
in one file, called header.php:



<html>

<head>

<title><?php echo $page['title'];?></title>

</head>

<body>

<!-- top menu bar -->

<table width="90%" border="0" cellspacing="5" cellpadding="5">

<tr>

<td><a href="#">Home</a></td>

<td><a href="#">Site Map</a></td>

<td><a href="#">Search</a></td>

<td><a href="#">Help</a></td>

</tr>

</table>

<!-- header ends -->


Next, create the footer with the copyright notice in a second file,
footer.php:



<!-- footer begins -->

<br />
<center>Your usage of this site is subject to its published <a href="tac.html">terms and conditions</a>. Data is copyright Big Company Inc, 1995-<?php echo date("Y", mktime()); ?></center>

</body>

</html>


Finally, create a script to display the main content of your site,
and include() the header and footer at appropriate places:



<?php

// create an array to set page-level variables
$page = array();

$page['title'] = 'Product Catalog';

/* once the file is imported, the variables set above will become available to it */

// include the page header

include('header.php');

?>



<!-- HTML content here -->

<?php

// include the page footer

include('footer.php');

?>


Now, when you run the script above, PHP will automatically read in
the header and footer files, merge them with the HTML content, and
display the complete page to you. Simple, isn’t it?

Notice that you can even write PHP code inside the files being
imported. When the file is first read in, the parser will look for
<?php...?> tags, and automatically execute the code inside it.
(If you’re familiar with JavaScript, you can use this feature to
replicate functionality similar to that of the onLoad() page event
handler in JavaScript.)

PHP also offers the require_once() and include_once()functions,
which ensure that a file which has already been read is not read again.
This can come in handy if you have a situation in which you want to
eliminate multiple reads of the same include file, either for
performance reasons or to avoid corruption of the variable space.

A quick note on the difference between the include() and
require()functions: the require()function returns a fatal error if the
named file cannot be found and halts script processing, while the
include() function returns a warning but allows script processing to
continue.


Writing to Ma

After everything you’ve just read, you’ve probably realized that
reading a file is not exactly brain surgery. So let’s proceed to
something slightly more difficult – writing to a file.

The steps involved in writing data to a file are almost identical to
those involved in reading it: open the file and obtain a file handle,
use the file handle to write data to it, and close the file. There are
two differences: first, you must fopen() the file in write mode ('w'
for write), and second, instead of using the fread() function to read
from the file handle, use the fwrite() function to write to it. Take a
look:



<?php

// set file to write
$file = '/tmp/dump.txt';

// open file

$fh = fopen($file, 'w') or die('Could not open file!');

// write to file

fwrite($fh, "Look, Ma, I wrote a file!
"
) or die('Could not write to file');

// close file

fclose($fh);

?>



When you run this script, it should create a file named dump.txt in
/tmp, and write a line of text to it, with a carriage return at the
end. Notice that double quotes are needed to convert
into a carriage
return.

The fopen(), fwrite() and fread() functions are all binary-safe,
which means you can use them on binary files without worrying about
damage to the file contents. Read more about many of the issues related
to binary-safe file manipulation on different platforms at http://www.php.net/manual/en/function.fopen.php.

If I’ve spoiled you by showing you the one-line shortcut functions
for file reads, let me damage you further by introducing you to the
file_put_contents() function, new in PHP 5.0, which takes a string and
writes it to a file in a single line of code.



<?php

// set file to write
$filename = '/tmp/dump.txt';

// write to file

file_put_contents($filename, "Look, Ma, I wrote a file!
"
) or die('Could not write to file');

?>



Bear in mind that the directory in which you’re trying to create the
file must exist before you can write to it. Forgetting this important
step is a common cause of script errors.


Information is Power

PHP also comes with a bunch of functions that allow you to test the
status of a file – for example to find out whether it exists, whether
it’s empty, whether it’s readable or writable, and whether it’s a
binary or text file. Of these, the most commonly used operator is the
file_exists() function, which is used to test for the existence of a
specific file.

Here’s an example which asks the user to enter the path to a file in
a Web form, and then returns a message displaying whether or not the
file exists:


<html>

<head>

</head>

<body>

<?php

// if form has not yet been submitted

// display input box

if (!isset($_POST['file'])) {

?>

    <form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">

    Enter file path <input type="text" name="file">

    </form>

<?php

}

// else process form input

else {

    
// check if file exists

    // display appropriate message

    
if (file_exists($_POST['file'])) {

        echo 'File exists!';

        }

    else {

        echo
'File does not exist!';

    }

}

?>

</body>

</html>


There are many more such functions. Here’s a brief list, followed by
an example that builds on the previous one to provide more information
on the file specified by the user.

  • is_dir() – returns a Boolean indicating whether the specified path
    is a directory
  • is_file() – returns a Boolean indicating whether the specified file
    is a regular file
  • is_link() – returns a Boolean indicating whether the specified file
    is a symbolic link
  • is_executable() – returns a Boolean indicating whether the
    specified file is executable
  • is_readable()– returns a Boolean indicating whether the specified
    file is readable
  • is_writable()– returns a Boolean indicating whether the specified
    file is writable
  • filesize() – gets size of file
  • filemtime() – gets last modification time of file
  • filamtime() – gets last access time of file
  • fileowner() – gets file owner
  • filegroup() – gets file group
  • fileperms() – gets file permissions
  • filetype() – gets file type

This script asks for a file name as input and uses the functions
above to return information on it.


<html>

<head>

</head>

<body>

<?php

/* if form has not yet been submitted, display input box */

if (!isset($_POST['file'])) {

?>

    <form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">

    Enter file path <input type="text" name="file">

    </form>

<?php

}

// else process form input

else {

    echo
'File name: <b>'.$_POST['file']  .'</b><br />';

    /* check if file exists and display appropriate message */

    
if (file_exists($_POST['file'])) {

        
// print file size

        
echo 'File size: '.filesize($_POST['file']).' bytes<br />';

        // print file owner

        
echo 'File owner: '.fileowner($_POST['file']).'<br />';

        
// print file group

        
echo 'File group: '.filegroup($_POST['file']).'<br />';

        // print file permissions

        
echo 'File permissions: '.fileperms($_POST['file']).'<br />';

        
// print file type

        
echo 'File type: '.filetype($_POST['file']).'<br />';

        // print file last access time

        
echo 'File last accessed on: '.date('Y-m-d', fileatime($_POST['file'])).'<br />';

        // print file last modification time

        
echo 'File last modified on: '.date('Y-m-d', filemtime($_POST['file'])).'<br />';

        // is it a directory?

        
if (is_dir($_POST['file'])) {

            echo
'File is a directory <br />';

        }

        
// is it a file?

        
if (is_file($_POST['file'])) {

            echo 'File is a regular file <br />';

        }

        
// is it a link?

        
if (is_link($_POST['file'])) {

            echo
'File is a symbolic link <br />';

        }

        // is it executable?

        
if (is_executable($_POST['file'])) {

            echo
'File is executable <br />';

        }

        
// is it readable?

        
if (is_readable($_POST['file'])) {

            echo 'File is readable <br />';

        }

        
// is it writable?

        
if (is_writable($_POST['file'])) {

            echo
'File is writable <br />';

        }

    }

    else {

        echo 'File does not exist! <br />';

    }

}

?>

</body>

</html>

And here’s what the output might look like:


Breaking Eggs

So now you know how to read a file, write to it, and test its
status. Let’s look at some examples of what you can do with this
new-found power.

Let’s go back to my Spanish omelette recipe. Let’s suppose I’m feeling
generous, and I decide that I’d like to hear what people really

think about my culinary skills. Since I have a bunch of recipes that
I’d like to share with people, and since they all look something like
this:

I need a quick way to convert them all into HTML so that they look
presentable on my Web site. We’ve already established that I’m lazy, so
fuggedaboutme re-creating the recipes in HTML. Instead, I’ll have PHP
do the heavy lifting for me:


<html>

<head></head>
<body>

<?php

// read recipe file into array

$data = file('/usr/local/stuff/that/should/be/elsewhere/omelette.txt') or die('Could not read file!');

/* first line contains title: read it into variable */

$title = $data[0];

// remove first line from array

array_shift($data);

?>

<h2><?php echo $title; ?></h2>

<?php

/* iterate over content and print it */

foreach ($data as $line) {

    echo nl2br($line);

}

?>

</body>

</html>


I’ve used the file() function to read the recipe into an array, and
assign the first line (the title) to a variable. That title is then
printed at the top of the page. Since the rest of the data is fairly
presentable as is, I can simply print the lines to the screen one after
the other. Line breaks are automatically handled for me by the
extremely cool nl2br() function, which converts regular text linebreaks
into the HTML equivalent, the <br /> tag. The end result: an
HTML-ized version of my recipe that the world can marvel at. Take a look:

If the elegance and creative simplicity of my Spanish omelette recipe
has left you speechless, I’m not surprised – many people feel that
way. Until you get your voice back: Ciao… and make sure you come back
to work through Part Six of PHP 101,
which discusses creating your own reusable functions.


Copyright Melonfire, 2004 (http://www.melonfire.com).
All rights reserved.