PHP Read File Tutorial

Introduction

What You’ll Learn

• How to read files using different PHP functions
• When to use file_get_contents() vs fgets()
• How to handle large files efficiently
• Real-world log file example
• Common mistakes and security tips

Why Read Files in PHP?

You may need to read files for:

• Displaying text content
• Reading configuration files
• Loading logs
• Processing uploaded files
• Fetching stored data

Reading files is essential in real-world PHP applications.

Using fopen() and fread()

The fopen() function opens a file, and fread() reads its content.

Example

$file = fopen("example.txt", "r");
$content = fread($file, filesize("example.txt"));
fclose($file);

echo $content;

Explanation

• fopen() opens the file in read mode
• filesize() gets the file size
• fread() reads the file content
• fclose() closes the file

After running this code, your browser will display the full content of your example.txt file. For example, if your file contains:

Hello, this is line one.
This is line two.
This is line three.

Then the output will be:

Hello, this is line one. This is line two. This is line three.

Using file_get_contents() (Recommended)

The file_get_contents() function reads the entire file in one line.

Example

$content = file_get_contents("example.txt");
echo $content;

If your example.txt contains:

Welcome to Div PHP Tutorials.
Learn PHP step by step.

Then the output will be:

Welcome to Div PHP Tutorials. Learn PHP step by step.

Why Use This?

• Simple and clean
• No need to open or close the file manually
• Best for small to medium files

Reading Files Line by Line (fgets)

To read a file line by line, use fgets().

Example

$file = fopen("example.txt", "r");

while (!feof($file)) {
    echo fgets($file) . "<br>";
}

fclose($file);

This is useful for large files.

If your example.txt contains three lines, the output will be:

Hello, this is line one.
This is line two.
This is line three.

Each line is printed on a new line in the browser because of the <br> tag added after each fgets() call.

Checking If a File Exists

Always check before reading a file.

Example

if (file_exists("example.txt")) {
    echo file_get_contents("example.txt");
} else {
    echo "File not found.";
}

This prevents errors and warnings.

💡 Why use this instead of file_get_contents()?

When a file is very large — for example, a log file with thousands of entries — loading the entire file into memory at once can slow down or crash your server. Reading line by line with fgets() processes one line at a time, keeping memory usage low.

Reading Files Using readfile()

The readfile() function outputs file content directly.

Example

readfile("example.txt");

Use this when you don’t need to process the content.

Comparison — Which Method Should You Use?

With four different ways to read a file in PHP, beginners often ask — which one should I use? Here is a simple comparison table to help you decide:

Simple rule for beginners:

• If you just need to read and display a file → use file_get_contents()
• If the file is very large → use fgets()
• If you just want to send a file to the browser → use readfile()
• If you need full control over how much you read → use fopen() + fread()

Real-World Example: Building a Simple Log File Viewer

To bring everything together, let us build a practical real-world example — a simple log file viewer that reads and displays the last 10 lines of a log file.

This is the kind of feature you might build for a WordPress admin panel or a custom PHP dashboard.

Step 1: Create a sample log file

Create a file called app_log.txt and add some sample log entries:

[2026-01-01 09:00:01] User Alice logged in successfully.
[2026-01-01 09:15:22] User Bob failed login attempt.
[2026-01-01 09:30:45] New post published: "PHP Tutorial".
[2026-01-01 10:00:00] User Alice logged out.
[2026-01-01 10:15:10] Database backup completed.

Step 2: Read and display the log file safely

php

<?php
$logFile = __DIR__ . "/app_log.txt";

// Step 1 — Check if the log file exists
if (!file_exists($logFile)) {
    echo "<p>No log file found.</p>";
    exit;
}

// Step 2 — Read all lines into an array
$lines = file($logFile, FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);

// Step 3 — Get the last 10 lines only
$lastLines = array_slice($lines, -10);

// Step 4 — Display each line
echo "<h2>Application Log (Last 10 Entries)</h2>";
echo "<ul>";
foreach ($lastLines as $line) {
    echo "<li>" . htmlspecialchars($line) . "</li>";
}
echo "</ul>";
?>

Output:

Application Log (Last 10 Entries)
- [2026-01-01 09:00:01] User Alice logged in successfully.
- [2026-01-01 09:15:22] User Bob failed login attempt.
- [2026-01-01 09:30:45] New post published: "PHP Tutorial".
- [2026-01-01 10:00:00] User Alice logged out.
- [2026-01-01 10:15:10] Database backup completed.

Why this example is important:

• It uses file() — a function that reads a file into an array, one line per element
• It uses array_slice() to get only the last 10 entries — efficient and practical
• It uses htmlspecialchars() to safely display the content — preventing XSS attacks
• It uses __DIR__ for a reliable file path
• It checks file existence before reading

This is real, production-level thinking applied to a beginner-friendly example.

Common Mistakes to Avoid

Mistake 1: Reading a File That Does Not Exist:
This is the most common mistake. If the file path is wrong or the file has been deleted, PHP will throw a warning and your script will fail. Always use file_exists(“example.txt”) to check if file exists or not.

Mistake 2: Forgetting to Close the File:
When you use fopen() to open a file, you must always close it with fclose() when you are done. Leaving files open wastes server resources and can cause unexpected behaviour in larger applications.

Mistake 3: Reading Very Large Files With file_get_contents():
file_get_contents() loads the entire file into memory at once. If you use it on a very large file — such as a server log with millions of lines — it can exhaust your server’s memory.

Mistake 4: Ignoring File Permissions:
PHP can only read a file if the server has permission to access it. If the file permissions are too restrictive, fopen() and other functions will fail silently or throw errors.

Security Tips

• Never read user-specified files directly
• Validate file paths
• Restrict access to sensitive files
• Avoid exposing configuration files

Summary

• PHP provides multiple ways to read files
• file_get_contents() is the easiest method
• Use fgets() for large files
• Always check file existence and permissions