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Filesystem

PHP File Handling

File handling is an important part of any web application. You often need to open and process a file for different tasks.

PHP has several functions for creating, reading, uploading, and editing files.

readfile()

The readfile() function reads a file and writes it to the output buffer.

Assume we have a text file called "webdictionary.txt", stored on the server, that looks like this: 

AJAX = Asynchronous JavaScript and XML
CSS = Cascading Style Sheets
HTML = Hyper Text Markup Language
PHP = PHP Hypertext Preprocessor
SQL = Structured Query Language
SVG = Scalable Vector Graphics
XML = EXtensible Markup Language

The PHP code to read the file and write it to the output buffer is as follows (the readfile() function returns the number of bytes read on success):

<?php
echo readfile("webdictionary.txt");
?>

The readfile() function is useful if all you want to do is open up a file and read its contents.

fopen()

A better method to open files is with the fopen() function. This function gives you more options than the readfile() function.

<?php
$myfile = fopen("webdictionary.txt", "r") or die("Unable to open file!");
echo fread($myfile, filesize("webdictionary.txt"));
fclose($myfile);
?>

The file may be opened in one of the following modes:

Modes Description
r Open a file for read only. File pointer starts at the beginning of the file
w Open a file for write only. Erases the contents of the file or creates a new file if it doesn't exist. File pointer starts at the beginning of the file
a Open a file for write only. The existing data in file is preserved. File pointer starts at the end of the file. Creates a new file if the file doesn't exist
x Creates a new file for write only. Returns FALSE and an error if file already exists
r+ Open a file for read/write. File pointer starts at the beginning of the file
w+ Open a file for read/write. Erases the contents of the file or creates a new file if it doesn't exist. File pointer starts at the beginning of the file
a+ Open a file for read/write. The existing data in file is preserved. File pointer starts at the end of the file. Creates a new file if the file doesn't exist
x+ Creates a new file for read/write. Returns FALSE and an error if file already exists

The fopen() function is also used to create a file. If you use fopen() on a file that does not exist, it will create it, given that the file is opened for writing (w) or appending (a).

<?php
$myfile = fopen("webdictionary.txt", "w") or die("Unable to open file!");
fwrite($myfile, "Hello World!");
fclose($myfile);
?>

File Permissions

If you are having errors when trying to get this code to run, check that you have granted your PHP file access to write information to the hard drive.

fread()

The fread() function reads from an open file.

The first parameter of fread() contains the name of the file to read from and the second parameter specifies the maximum number of bytes to read.

The following PHP code reads the "webdictionary.txt" file to the end: 

fread($myfile,filesize("webdictionary.txt"));

fwrite()

The fwrite() function is used to write to a file.

The first parameter of fwrite() contains the name of the file to write to and the second parameter is the string to be written. 

<?php
$myfile = fopen("newfile.txt", "w") or die("Unable to open file!");
$txt = "John Doe\n";
fwrite($myfile, $txt);
$txt = "Jane Doe\n";
fwrite($myfile, $txt);
fclose($myfile);
?>

fclose()

The fclose() function is used to close an open file.

It's a good programming practice to close all files after you have finished with them.

The fclose() requires the name of the file (or a variable that holds the filename) we want to close: 

<?php
$myfile = fopen("webdictionary.txt", "r");
// some code to be executed....
fclose($myfile);
?>

fgets()

The fgets() function is used to read a single line from a file.

<?php
$myfile = fopen("webdictionary.txt", "r") or die("Unable to open file!");
echo fgets($myfile);
fclose($myfile);
?>

After a call to the fgets() function, the file pointer has moved to the next line.

feof()

The feof() function checks if the "end-of-file" (EOF) has been reached.

The feof() function is useful for looping through data of unknown length.

<?php
$myfile = fopen("webdictionary.txt", "r") or die("Unable to open file!");
// Output one line until end-of-file
while(!feof($myfile)) {
  echo fgets($myfile) . "<br>";
}
fclose($myfile);
?>

fgetc()

The fgetc() function is used to read a single character from a file.

<?php
$myfile = fopen("webdictionary.txt", "r") or die("Unable to open file!");
// Output one character until end-of-file
while(!feof($myfile)) {
  echo fgetc($myfile);
}
fclose($myfile);
?>

After a call to the fgetc() function, the file pointer moves to the next character.

PHP File Upload

With PHP, it is easy to upload files to the server.

Configure The "php.ini" File

First, ensure that PHP is configured to allow file uploads.

In your "php.ini" file, search for the file_uploads directive, and set it to On:

file_uploads = On

Create The HTML Form

<!DOCTYPE html>
<html>
<body>

<form action="upload.php" method="post" enctype="multipart/form-data">
  Select image to upload:
  <input type="file" name="fileToUpload" id="fileToUpload">
  <input type="submit" value="Upload Image" name="submit">
</form>

</body>
</html>

Some rules to follow for the HTML form above:

  • Make sure that the form uses method="post"
  • The form also needs the following attribute: enctype="multipart/form-data". It specifies which content-type to use when submitting the form

Without the requirements above, the file upload will not work.

Other things to notice:

  • The type="file" attribute of the input tag shows the input field as a file-select control, with a "Browse" button next to the input control

The form above sends data to a file called "upload.php", which we will create next.

Create The Upload File PHP Script

The "upload.php" file contains the code for uploading a file:

<?php
$target_dir = "uploads/";
$target_file = $target_dir . basename($_FILES["fileToUpload"]["name"]);
$uploadOk = 1;
$imageFileType = strtolower(pathinfo($target_file,PATHINFO_EXTENSION));
// Check if image file is a actual image or fake image
if(isset($_POST["submit"])) {
  $check = getimagesize($_FILES["fileToUpload"]["tmp_name"]);
  if($check !== false) {
    echo "File is an image - " . $check["mime"] . ".";
    $uploadOk = 1;
  } else {
    echo "File is not an image.";
    $uploadOk = 0;
  }
}
?>

PHP script explained:

  • $target_dir = "uploads/" - specifies the directory where the file is going to be placed
  • $target_file specifies the path of the file to be uploaded
  • $uploadOk=1 is not used yet (will be used later)
  • $imageFileType holds the file extension of the file (in lower case)
  • Next, check if the image file is an actual image or a fake image

You will need to create a new directory called "uploads" in the directory where "upload.php" file resides. The uploaded files will be saved there.

Check if File Already Exists

Now we can add some restrictions.

First, we will check if the file already exists in the "uploads" folder. If it does, an error message is displayed, and $uploadOk is set to 0:

// Check if file already exists
if (file_exists($target_file)) {
  echo "Sorry, file already exists.";
  $uploadOk = 0;
}
?>

Limit File Size

The file input field in our HTML form above is named "fileToUpload".

Now, we want to check the size of the file. If the file is larger than 500KB, an error message is displayed, and $uploadOk is set to 0:

// Check file size
if ($_FILES["fileToUpload"]["size"] > 500000) {
  echo "Sorry, your file is too large.";
  $uploadOk = 0;
}
?>

Limit File Type

The code below only allows users to upload JPG, JPEG, PNG, and GIF files. All other file types gives an error message before setting $uploadOk to 0:

// Allow certain file formats
if($imageFileType != "jpg" && $imageFileType != "png" && $imageFileType != "jpeg"
&& $imageFileType != "gif" ) {
  echo "Sorry, only JPG, JPEG, PNG & GIF files are allowed.";
  $uploadOk = 0;
}
?>

Complete Upload File PHP Script

The complete "upload.php" file now looks like this:

<?php
$target_dir = "uploads/";
$target_file = $target_dir . basename($_FILES["fileToUpload"]["name"]);
$uploadOk = 1;
$imageFileType = strtolower(pathinfo($target_file,PATHINFO_EXTENSION));

// Check if image file is a actual image or fake image
if(isset($_POST["submit"])) {
  $check = getimagesize($_FILES["fileToUpload"]["tmp_name"]);
  if($check !== false) {
    echo "File is an image - " . $check["mime"] . ".";
    $uploadOk = 1;
  } else {
    echo "File is not an image.";
    $uploadOk = 0;
  }
}

// Check if file already exists
if (file_exists($target_file)) {
  echo "Sorry, file already exists.";
  $uploadOk = 0;
}

// Check file size
if ($_FILES["fileToUpload"]["size"] > 500000) {
  echo "Sorry, your file is too large.";
  $uploadOk = 0;
}

// Allow certain file formats
if($imageFileType != "jpg" && $imageFileType != "png" && $imageFileType != "jpeg"
&& $imageFileType != "gif" ) {
  echo "Sorry, only JPG, JPEG, PNG & GIF files are allowed.";
  $uploadOk = 0;
}

// Check if $uploadOk is set to 0 by an error
if ($uploadOk == 0) {
  echo "Sorry, your file was not uploaded.";
// if everything is ok, try to upload file
} else {
  if (move_uploaded_file($_FILES["fileToUpload"]["tmp_name"], $target_file)) {
    echo "The file ". htmlspecialchars( basename( $_FILES["fileToUpload"]["name"])). " has been uploaded.";
  } else {
    echo "Sorry, there was an error uploading your file.";
  }
}
?>

PHP Directory Functions

Function Description
chdir() Changes the current directory
chroot() Changes the root directory
closedir() Closes a directory handle
dir() Returns an instance of the Directory class
getcwd() Returns the current working directory
opendir() Opens a directory handle
readdir() Returns an entry from a directory handle
rewinddir() Resets a directory handle
scandir() Returns an array of files and directories of a specified directory

chdir()

The chdir() function changes the current working directory.

<?php
// Get current directory
echo getcwd() . "<br>";

// Change directory
chdir("images");

// Get current directory
echo getcwd();
?>

chroot()

The chroot() function changes the root directory.

<?php
// Change root directory
chroot("/path/to/chroot/");

// Get current directory
echo getcwd();
?>

closedir()

The closedir() function closes a directory handle.

<?php
$dir = "/images/";

// Open a directory, and read its contents
if (is_dir($dir)){
  if ($dh = opendir($dir)){
    while (($file = readdir($dh)) !== false){
      echo "filename:" . $file . "<br>";
    }
    closedir($dh);
  }
}
?>

dir()

The dir() function returns an instance of the Directory class.

<?php
$d = dir(getcwd());

echo "Handle: " . $d->handle . "<br>";
echo "Path: " . $d->path . "<br>";

while (($file = $d->read()) !== false){
  echo "filename: " . $file . "<br>";
}
$d->close();
?>

Handle: Resource id #2
Path: /etc/php
filename: .
filename: ..
filename: ajax.gif
filename: books.xml
filename: cdcatalog.xml
filename: cd_catalog.xml
filename: default.asp
filename: demo_array.asp
filename: demo_array.htm
...
...
...

getcwd()

The getcwd() function returns the current working directory.

<?php
echo getcwd();
?>

/home/username/public_html

opendir()

The opendir() function opens a directory handle.

<?php
$dir = "/images/";

// Open a directory, and read its contents
if (is_dir($dir)){
  if ($dh = opendir($dir)){
    while (($file = readdir($dh)) !== false){
      echo "filename:" . $file . "<br>";
    }
    closedir($dh);
  }
}
?>

readdir()

The readdir() function returns an entry from a directory handle.

<?php
$dir = "/images/";

// Open a directory, and read its contents
if (is_dir($dir)){
  if ($dh = opendir($dir)){
    while (($file = readdir($dh)) !== false){
      echo "filename:" . $file . "<br>";
    }
    closedir($dh);
  }
}
?>

rewinddir()

The rewinddir() function resets a directory handle.

<?php
$dir = "/images/";

// Open a directory, and read its contents
if (is_dir($dir)){
  if ($dh = opendir($dir)){
    // List files in images directory
    while (($file = readdir($dh)) !== false){
      echo "filename:" . $file . "<br>";
    }
    rewinddir();
    // List once again files in images directory
    while (($file = readdir($dh)) !== false){
      echo "filename:" . $file . "<br>";
    }
    closedir($dh);
  }
}
?>

scandir()

The scandir() function returns an array of files and directories of a specified directory.

<?php
$dir = "/images/";

// Sort in ascending order - this is default
$a = scandir($dir);

// Sort in descending order
$b = scandir($dir,1);

print_r($a);
print_r($b);
?>