File handling in PHP involves reading from and writing to files on the server. PHP provides a set of functions for manipulating files, allowing you to perform operations like creating, opening, reading, writing, and deleting files. Here’s a comprehensive overview of file handling in PHP:

Basic File Operations

1. Opening a File

You use fopen() to open a file and obtain a file handle. The file handle is then used in other file operations.

Syntax:

$fileHandle = fopen(string $filename, string $mode);

• $filename: The path to the file.
• $mode: The mode in which to open the file (e.g., r, w, a).

Example:

<?php
$fileHandle = fopen("example.txt", "r"); // Open file for reading
if ($fileHandle) {
    echo "File opened successfully.";
} else {
    echo "Failed to open file.";
}
?>

2. Reading from a File

Once a file is opened, you can read its contents using functions like fread(), fgets(), or file_get_contents().

• fread(): Reads a specified number of bytes from a file.

  Example:

  <?php
  $fileHandle = fopen("example.txt", "r");
  $content = fread($fileHandle, filesize("example.txt")); // Read the entire file
  fclose($fileHandle);
  echo $content;
  ?>
  

• fgets(): Reads a single line from a file.

  Example:

  <?php
  $fileHandle = fopen("example.txt", "r");
  while (($line = fgets($fileHandle)) !== false) {
      echo $line . "<br>";
  }
  fclose($fileHandle);
  ?>
  

• file_get_contents(): Reads the entire file into a string.

  Example:

  <?php
  $content = file_get_contents("example.txt");
  echo $content;
  ?>
  

3. Writing to a File

You can write to a file using fwrite() or file_put_contents().

• fwrite(): Writes a string to a file.

  Example:

  <?php
  $fileHandle = fopen("example.txt", "w");
  fwrite($fileHandle, "Hello, World!");
  fclose($fileHandle);
  ?>
  

• file_put_contents(): Writes data to a file. It is a simpler way to write data to a file and can also create the file if it does not exist.

  Example:

  <?php
  file_put_contents("example.txt", "Hello, World!");
  ?>
  

4. Appending to a File

To add data to the end of a file without overwriting its existing content, use the a mode in fopen().

Example:

<?php
$fileHandle = fopen("example.txt", "a");
fwrite($fileHandle, "Appended text.");
fclose($fileHandle);
?>

5. Closing a File

After performing file operations, close the file using fclose() to free up system resources.

Example:

<?php
$fileHandle = fopen("example.txt", "r");
// Perform file operations
fclose($fileHandle); // Close the file
?>

File Handling Functions

• file_exists($filename): Checks if a file or directory exists.

  Example:

  <?php
  if (file_exists("example.txt")) {
      echo "File exists.";
  } else {
      echo "File does not exist.";
  }
  ?>
  

• filesize($filename): Returns the size of a file in bytes.

  Example:

  <?php
  echo "File size: " . filesize("example.txt") . " bytes.";
  ?>
  

• fopen() Modes:

  • r - Read-only. Opens the file for reading.
  • w - Write-only. Opens the file for writing (creates a new file or truncates an existing file).
  • a - Append-only. Opens the file for writing (appends data to the end).
  • x - Write-only. Creates a new file, returns false if file already exists.

Error Handling

When working with files, always check if file operations are successful and handle errors gracefully.

Example:

<?php
$fileHandle = @fopen("example.txt", "r");
if (!$fileHandle) {
    die("Failed to open file.");
}
$content = fread($fileHandle, filesize("example.txt"));
fclose($fileHandle);
echo $content;
?>

File Uploads

To handle file uploads in PHP, use the $_FILES superglobal array. The form must use multipart/form-data encoding.

Example HTML Form:

<form action="upload.php" method="post" enctype="multipart/form-data">
    <input type="file" name="fileToUpload">
    <input type="submit" value="Upload File">
</form>

Example PHP Script (upload.php):

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

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

// Check file size (limit: 5MB)
if ($_FILES["fileToUpload"]["size"] > 5000000) {
    echo "Sorry, your file is too large.";
    $uploadOk = 0;
}

// Allow certain file formats
if ($fileType != "jpg" && $fileType != "png" && $fileType != "jpeg" && $fileType != "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"], $targetFile)) {
        echo "The file ". htmlspecialchars(basename($_FILES["fileToUpload"]["name"])) . " has been uploaded.";
    } else {
        echo "Sorry, there was an error uploading your file.";
    }
}
?>