File Handling

Previous Next

PHP can read and write files directly on the server — text logs, CSV exports, cache files, or small notes like the demo below. This page covers opening files with fopen(), reading and writing content, checking whether a file exists before touching it, and cleaning up with fclose() or unlink().

Careful: Never build a file path directly from user input. Always keep uploaded/generated files inside a dedicated folder (like demo-data/ below) so a visitor can never read or overwrite an arbitrary file on your server.

1) Opening a File with fopen()

fopen() opens a file and returns a file handle (a resource) you use for subsequent reads/writes. The second argument is the mode:

Mode	Meaning
`r`	Read only. Pointer starts at the beginning. Fails if file doesn't exist.
`w`	Write only. Erases existing content (or creates the file).
`a`	Write only, appends to the end. Creates the file if missing.
`r+`	Read and write. Pointer starts at the beginning; doesn't erase content.

<?php
  $handle = fopen('log.txt', 'a');
  if ($handle === false) {
    die('Could not open file.');
  }
  fwrite($handle, "New line\n");
  fclose($handle); // always close what you open
?>

2) Reading Files

For most small/medium files, the simplest approach is file_get_contents() — it opens, reads the whole file, and closes it in one call.

<?php
  $contents = file_get_contents('log.txt');
  echo $contents;
?>

2.1 Reading line-by-line with fgets()

<?php
  $handle = fopen('log.txt', 'r');
  while ($handle && !feof($handle)) {
    $line = fgets($handle);
    echo $line;
  }
  fclose($handle);
?>

2.2 Reading the whole file into an array

<?php
  // Each element is one line, without the trailing newline
  $lines = file('log.txt', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
  $lastFive = array_slice($lines, -5);
?>

3) Writing & Appending with file_put_contents()

file_put_contents() is a shortcut that opens, writes, and closes the file for you in one call — no need to manage a handle manually.

<?php
  // Overwrite the file completely
  file_put_contents('log.txt', "Fresh start\n");

  // Append instead of overwrite, and lock while writing
  file_put_contents('log.txt', "Another line\n", FILE_APPEND | LOCK_EX);
?>

Tip: FILE_APPEND keeps old content and adds to the end (same idea as opening with mode a). Without it, file_put_contents() behaves like mode w and erases what was there.

4) Checking Before You Touch a File

Always check a file's state before reading, writing, or deleting it — this avoids warnings and lets you handle "file not found" gracefully.

<?php
  $path = __DIR__ . '/demo-data/notes.txt';

  if (!file_exists($path)) {
    echo 'No notes saved yet.';
  } elseif (!is_readable($path)) {
    echo 'Notes file exists but cannot be read.';
  } else {
    echo file_get_contents($path);
  }
?>

Function	Returns
`file_exists($path)`	`true` if a file or directory exists at that path
`is_readable($path)`	`true` if PHP has permission to read it
`is_writable($path)`	`true` if PHP has permission to write to it

5) Deleting a File with unlink()

<?php
  $path = __DIR__ . '/demo-data/notes.txt';
  if (file_exists($path)) {
    unlink($path); // permanently removes the file
  }
?>

Try File Read/Write Basics »

6) Working Demo: Save & Read Notes (Real File I/O)

Type a short note below and click Save Note. The server appends it (with a timestamp) to a demo file at php/demo-data/notes.txt using file_put_contents(), then the page reads that file back and shows the last 5 notes — a real, working, server-side file operation, safely contained in its own folder.

Last 5 Notes

No notes saved yet — be the first!

7) Best Practices & Common Mistakes

Issue	Problem	Fix
Using raw user input in a path	Path traversal (`../../etc/passwd`)	Restrict to a fixed folder; never trust `$_GET`/`$_POST` for file paths
Forgetting `FILE_APPEND`	Mode `w`-style writes silently erase old data	Use `FILE_APPEND` or open with mode `a`
Not checking `file_exists()`	Warnings / crashes on first run	Check existence before `fopen()`/`file_get_contents()`
Concurrent writes without a lock	Corrupted/interleaved lines	Add `LOCK_EX` to `file_put_contents()`
Leaving handles open	Resource leaks on busy servers	Always `fclose()`, or prefer `file_get_contents`/`file_put_contents`

8) Practice Tasks

Write a script that appends a visitor's IP address and timestamp to a log file on every load.
Read a log file back and count how many lines it has using count(file($path)).
Write a function safe_read($path) that returns an empty string if the file doesn't exist or isn't readable.
Add a "download notes" link that streams the demo file's contents as a plain-text response.

Next: Continue with Sessions — store data per-visitor on the server between page loads.

Previous Next