PHP File Handling Exercises: Logs, Counters and CSV

Exercise 1: count the lines

Create a file with five lines of text, then print how many lines it has and the length of the longest one.

Show a possible solution

index.php

PHP

<?php
file_put_contents("poem.txt", "one\ntwo words\nthree\nfour four\nfive\n");

$lines = file("poem.txt", FILE_IGNORE_NEW_LINES);

$longest = max(array_map("strlen", $lines));

echo count($lines) . " lines, longest has $longest characters";

Output

OUTPUT

5 lines, longest has 9 characters

Exercise 2: a simple log reader

A log file has lines like 2026-01-05 ERROR Disk full. Print only the lines that contain ERROR, and how many there are.

Show a possible solution

index.php

PHP

<?php
file_put_contents("app.log",
    "2026-01-05 INFO Started\n" .
    "2026-01-05 ERROR Disk full\n" .
    "2026-01-06 INFO Saved\n" .
    "2026-01-06 ERROR Timeout\n"
);

$errors = [];
$handle = fopen("app.log", "r");

while (($line = fgets($handle)) !== false) {
    if (str_contains($line, " ERROR ")) {
        $errors[] = trim($line);
    }
}

fclose($handle);

echo implode("\n", $errors) . "\n";
echo count($errors) . " errors";

Output

OUTPUT

1
2
3

2026-01-05 ERROR Disk full
2026-01-06 ERROR Timeout
2 errors

Exercise 3: total a CSV column

A CSV file sales.csv has the columns item,price,qty. Print the total of price times qty.

Show a possible solution

index.php

PHP

<?php
file_put_contents("sales.csv", "item,price,qty\nPen,12,5\nBook,250,2\nBag,799,1\n");

$handle = fopen("sales.csv", "r");
fgetcsv($handle, 0, ",", '"', "\\");   // skip the header

$total = 0;

while (($row = fgetcsv($handle, 0, ",", '"', "\\")) !== false) {
    [$item, $price, $qty] = $row;
    $total += (float) $price * (int) $qty;
}

fclose($handle);

echo "Total: $total";

Output

OUTPUT

Total: 1359

Exercise 4: a safe guestbook

Write a function addEntry(string $name, string $message): void that appends one line to guestbook.txt in the form name: message. New lines inside the text must not create extra entries. Show the file after adding an entry with a line break in the message.

Show a possible solution

index.php

PHP

<?php
function addEntry(string $name, string $message): void
{
    $clean = fn(string $text): string => trim(str_replace(["\r", "\n"], " ", $text));

    $line = $clean($name) . ": " . $clean($message) . PHP_EOL;

    file_put_contents("guestbook.txt", $line, FILE_APPEND | LOCK_EX);
}

addEntry("Ana", "Hello!");
addEntry("Ben", "First line\nSecond line");

echo file_get_contents("guestbook.txt");

Output

OUTPUT

1
2

Ana: Hello!
Ben: First line Second line

Exercise 5: list and clean up

Create three .tmp files in a folder called cache, list them with glob(), then delete them all and show how many files are left.

Show a possible solution

index.php

PHP

<?php
mkdir("cache");

foreach (["a", "b", "c"] as $name) {
    file_put_contents("cache/$name.tmp", "data");
}

$files = glob("cache/*.tmp");
echo count($files) . " files: " . implode(", ", array_map("basename", $files)) . "\n";

foreach ($files as $file) {
    unlink($file);
}

echo count(glob("cache/*.tmp")) . " files left";

Output

OUTPUT

1
2

3 files: a.tmp, b.tmp, c.tmp
0 files left