PHP File Handling: Reading, Writing, Appending & Stream Operations

Beyond databases, web applications frequently interact directly with server filesystems—such as writing transaction audit logs, reading configuration files, parsing CSV spreadsheets, and caching HTML pages. PHP provides robust, C-level File Handling functions that allow you to create, read, write, append, and lock files on the server safely.

File Open Modes Reference Table (fopen)

When you open a file handle with fopen($filename, $mode), the mode dictates read/write permissions and cursor positioning:

Method 1: Writing & Appending Data (fwrite)

<?php
    $logFile = "student_access.log";

    // Open file in append mode ('a')
    $handle = fopen($logFile, "a");

    if ($handle) {
        $timestamp = date("Y-m-d H:i:s");
        $logEntry = "[$timestamp] User Vikram logged in from IP 192.168.1.10\n";

        // Write log entry to file
        fwrite($handle, $logEntry);

        // Always close open file streams!
        fclose($handle);
        echo "Log entry appended successfully.";
    } else {
        echo "Error: Unable to open file for writing.";
    }
?>

Method 2: Reading Line-by-Line (fgets and feof)

For large files that exceed PHP's memory limit, reading line-by-line with fgets() is the professional practice:

<?php
    $handle = fopen("student_access.log", "r");

    if ($handle) {
        echo "<h4>Access Audit Trail:</h4><pre>";
        // feof() checks if end-of-file has been reached
        while (!feof($handle)) {
            $line = fgets($handle); // Reads one line at a time
            echo htmlspecialchars($line);
        }
        echo "</pre>";
        fclose($handle);
    }
?>

Modern Shorthands: file_get_contents() & file_put_contents()

When you simply want to read or write an entire file in one clean line of code:

<?php
    // Read entire file into string
    $content = file_get_contents("notes.txt");

    // Write string to file (FILE_APPEND flag appends rather than overwriting)
    file_put_contents("notes.txt", "New lecture notes added.\n", FILE_APPEND | LOCK_EX);
?>

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