Reading and Writing Files

A diary remembers what happened yesterday, even though you slept in between. Files are your program's diary.

In How PHP Runs, you learned that PHP forgets everything after each request. Sessions remember one visitor for a while. But to remember things for everyone, and for good, like every message in a guestbook, you need to save them somewhere lasting. The simplest place is a file.

Writing and reading a whole file

Two functions do most of the work:

<?php
file_put_contents("note.txt", "Buy rice and eggs.\n");

$text = file_get_contents("note.txt");
echo "The note says: $text";

The note says: Buy rice and eggs.

• file_put_contents(file, text) writes the text to the file. It creates the file if it's missing, and replaces everything in it if it exists.
• file_get_contents(file) reads the whole file and returns it as a string.

A path like "note.txt" is looked up from where PHP is running. As in Splitting Code with include and require, __DIR__ . "/note.txt" is safer in real projects, because it always means "next to this PHP file."

Adding to the end

To add to a file instead of replacing it, pass the FILE_APPEND flag:

<?php
file_put_contents("log.txt", "Started\n");
file_put_contents("log.txt", "Saved order 1\n", FILE_APPEND);
file_put_contents("log.txt", "Saved order 2\n", FILE_APPEND);

echo file_get_contents("log.txt");

Started
Saved order 1
Saved order 2

On a busy website, two visitors might write at the same moment, and their lines could get mixed up. Adding LOCK_EX makes each write wait its turn: FILE_APPEND | LOCK_EX.

Reading line by line

file() reads a file into an array, one item per line. Add two flags to drop the line endings and skip empty lines:

<?php
file_put_contents("shopping.txt", "rice\neggs\n\nmangoes\n");

$items = file("shopping.txt", FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
echo count($items) . " items\n";
foreach ($items as $i => $item) {
    echo ($i + 1) . ". $item\n";
}

3 items
1. rice
2. eggs
3. mangoes

For very large files, reading everything at once uses a lot of memory. Then you'd open the file and read one line at a time:

<?php
file_put_contents("big.txt", "line one\nline two\n");

$handle = fopen("big.txt", "r");
while (($line = fgets($handle)) !== false) {
    echo "Read: " . trim($line) . "\n";
}
fclose($handle);

Read: line one
Read: line two

• fopen(file, "r") opens a file and gives you a handle, a connection to it. "r" means read; "w" means write (replacing), and "a" means append.
• fgets reads the next line, and returns false at the end of the file.
• fclose closes the file when you're done.

When the file isn't there

Reading a file that doesn't exist gives a warning, and returns false:

<?php
$text = file_get_contents("missing.txt");
// error: Warning: file_get_contents(missing.txt): Failed to open stream: No such file or directory

Check first with file_exists():

<?php
$file = "settings.txt";
if (file_exists($file)) {
    echo file_get_contents($file);
} else {
    echo "No settings saved yet.\n";
}

No settings saved yet.

Other useful checks and actions: is_file(), is_dir(), filesize(), unlink() to delete a file, and mkdir() to make a folder.

CSV: spreadsheet-friendly data

A CSV file (comma-separated values) stores a table as text: one row per line, with commas between the values. Spreadsheet programs like Excel and Google Sheets open it directly. PHP reads and writes it with fputcsv and fgetcsv:

<?php
$students = [
    ["name", "grade", "note"],
    ["Maria", 92, "Top of class"],
    ["Ben", 85, "Great, improving"],
];

$handle = fopen("grades.csv", "w");
foreach ($students as $row) {
    fputcsv($handle, $row, escape: "");
}
fclose($handle);

echo file_get_contents("grades.csv");

name,grade,note
Maria,92,"Top of class"
Ben,85,"Great, improving"

fputcsv adds quotes where needed, so the comma inside "Great, improving" doesn't split it into two columns. Reading it back:

<?php
$handle = fopen("grades.csv", "r");
$header = fgetcsv($handle, escape: "");
while (($row = fgetcsv($handle, escape: "")) !== false) {
    echo "$row[0] got $row[1]\n";
}
fclose($handle);

Maria got 92
Ben got 85

The first fgetcsv call reads the header row into $header, so the loop starts with the real data.

What's the escape: ""? The CSV functions have an old, non-standard way of treating backslashes, and PHP 8.4 and later print a "Deprecated" notice unless you choose. An empty string turns that old behavior off, which is what you want. Always include it.

Every value fgetcsv reads is a string, even "92", just like form data.

Files and web security

Files on a web server need care:

• Keep data files out of the public folder. If grades.csv sits next to your pages, anyone can download it at yoursite.com/grades.csv. Put data one folder up, or in a folder the web server doesn't serve.
• Never build a file path from user input directly. A visitor asking for ?file=../../passwords.txt could read files you never meant to share. If a visitor chooses a file, check their choice against a list of allowed names.
• Escape file contents with htmlspecialchars when you show them in a page, since they may contain whatever someone typed.

For anything beyond simple logs and small lists, a database is the better choice. It handles many visitors at once, and searches quickly. That's coming up in Databases with PDO.

Try it

A guestbook saves messages to a CSV file, then shows them. Predict what it prints.

Running PHP here

Running PHP right in the browser is coming to Syntaxia soon. For now, you can read and edit the code here. If you have PHP installed on your computer (see Setting Up), save it as index.php and run it with php index.php.

Check your prediction

Entries: 3
Second line in the file: Ben,"Hello, from Cebu",2026
- Maria wrote: Lovely site!
- Ben wrote: Hello, from Cebu
- Joy wrote: See you soon
no missing.csv

The first file_put_contents empties the file, so every run starts fresh. "a" opens it for appending, one row per entry, with today's year added. Ben's message has a comma, so fputcsv wraps it in quotes in the file, and fgetcsv removes them again when reading. [$name, $message] = $row; unpacks the first two values of each row. (Your year may differ.)

Try it yourself

1. Remove the file_put_contents($file, ""); line and run the script three times. How many entries are there now?
2. Add a function countEntries(string $file): int that returns how many entries the guestbook has, and returns 0 if the file doesn't exist.
3. Write a script that reads grades.csv from this lesson and prints the class average.

Check your understanding

What does file_put_contents("a.txt", "hi") do if a.txt already has text in it?

Adds hi to the end

Replaces everything in the file with hi

Gives an error

Does nothing

Why shouldn't a data file sit in your website's public folder?

PHP cannot read it there

It makes the site slower

Files there are deleted every day

Anyone could download it by typing its address

What does fgets return when there are no more lines?

false

An empty string

null

0

Up next

CSV is great for tables, but what about nested data, like a list of orders where each order has its own list of items? For that, there's the format every web API speaks: Working with JSON.