File Handling 📂

<?php
// The "quick" pair: two functions that do a whole job in one line each.
// Work inside the system temp directory so this runs anywhere safely.
$file = sys_get_temp_dir() . "/notes.txt";

// file_put_contents() CREATES the file (or OVERWRITES it if it exists)
// and writes the whole string in one go. It returns the number of bytes written.
$bytes = file_put_contents($file, "Buy milk\nWalk the dog\n");
echo "Wrote $bytes bytes.\n";          // Wrote 22 bytes.

// FILE_APPEND adds to the END instead of wiping the file first.
file_put_contents($file, "Pay rent\n", FILE_APPEND);

// file_get_contents() reads the WHOLE file back as one string.
$content = file_get_contents($file);
echo "--- file contents ---\n";
echo $content;                          // prints all three lines
?>

Wrote 22 bytes.
--- file contents ---
Buy milk
Walk the dog
Pay rent

<?php
// The "detailed" way: open a HANDLE, do several operations, then close it.
// A handle (also called a stream) is a live connection to the file you keep open.
$file = sys_get_temp_dir() . "/log.txt";

// fopen() returns a handle. The MODE (second argument) decides what you may do:
//   "r"  read only   — file must exist
//   "w"  write only  — TRUNCATES (empties) the file, or creates it
//   "a"  append only — writes go to the END, never erases
$handle = fopen($file, "w");            // "w" => start with an empty file
fwrite($handle, "line one\n");          // write a string to the handle
fwrite($handle, "line two\n");
fclose($handle);                        // ALWAYS close when finished

// Re-open in "a" (append) mode so we keep the two lines above.
$handle = fopen($file, "a");
fwrite($handle, "line three\n");
fclose($handle);

echo file_get_contents($file);          // three lines, in order
?>

line one
line two
line three

<?php
// Reading a big file line by line keeps memory low — you hold ONE line at a time,
// not the whole file. This is the right tool for large logs or data dumps.
$file = sys_get_temp_dir() . "/cities.txt";
file_put_contents($file, "London\nParis\nTokyo\n");

// Open for reading. fgets() returns the NEXT line (including its \n), or false at the end.
$handle = fopen($file, "r");
$n = 1;
while (($line = fgets($handle)) !== false) {   // loop until fgets() returns false
    echo $n . ": " . trim($line) . "\n";       // trim() removes the trailing newline
    $n++;
}
fclose($handle);

// feof() means "end of file" — true once you've read past the last line.
echo "Reached end of file: " . var_export(feof($handle = fopen($file, "r")), true) . "\n";
fclose($handle);

// Shortcut: file() reads the WHOLE file into an array, one line per element.
$lines = file($file, FILE_IGNORE_NEW_LINES);   // flag drops the trailing \n on each line
echo "file() gave " . count($lines) . " lines; the 2nd is '" . $lines[1] . "'.\n";
?>

1: London
2: Paris
3: Tokyo
Reached end of file: false
file() gave 3 lines; the 2nd is 'Paris'.

<?php
// NEVER assume a file is there. Check before you read so you fail gracefully
// instead of crashing with a warning.
$file = sys_get_temp_dir() . "/maybe.txt";

if (!file_exists($file)) {
    echo "No file yet — creating one.\n";
    file_put_contents($file, "now it exists");
}

// file_exists() = is there anything at this path?
// is_readable()  = am I allowed to read it?
// is_writable()  = am I allowed to write to it?
if (file_exists($file) && is_readable($file)) {
    echo "Safe to read: " . file_get_contents($file) . "\n";
} else {
    echo "Cannot read the file.\n";
}

// Handy facts about the path (these work even on names, no file needed):
echo "Size:      " . filesize($file) . " bytes\n";
echo "Extension: " . pathinfo($file, PATHINFO_EXTENSION) . "\n";   // txt
echo "Basename:  " . basename($file) . "\n";                       // maybe.txt
?>

No file yet — creating one.
Safe to read: now it exists
Size:      13 bytes
Extension: txt
Basename:  maybe.txt

<?php
// CSV (comma-separated values) is the universal spreadsheet/export format.
// Use fputcsv()/fgetcsv() instead of joining strings yourself — they handle
// commas, quotes and escaping inside a value correctly.
$file = sys_get_temp_dir() . "/people.csv";

$rows = [
    ["Name", "Email", "Age"],                  // header row
    ["Alice", "alice@example.com", 28],
    ["Bob", "bob, jr@example.com", 34],        // note the comma INSIDE the email
];

// WRITE the CSV.
$out = fopen($file, "w");
foreach ($rows as $row) {
    fputcsv($out, $row);                       // one array => one CSV line
}
fclose($out);

// READ it back. fgetcsv() turns each line into an array, splitting on commas
// but respecting quotes — so "bob, jr@example.com" stays a single field.
$in = fopen($file, "r");
$headers = fgetcsv($in);                        // first line = column names
echo implode(" | ", $headers) . "\n";
while (($data = fgetcsv($in)) !== false) {
    echo $data[0] . " is " . $data[2] . "\n";   // Name is Age
}
fclose($in);
?>

Name | Email | Age
Alice is 28
Bob is 34

<?php
// 🎯 YOUR TURN — build a tiny log that GROWS instead of being overwritten.
// Fill in each blank marked ___ using the 👉 hint, then run it.
$file = sys_get_temp_dir() . "/visits.log";

// Start clean so the demo is repeatable.
file_put_contents($file, "");

// 1) Append three lines. The flag that adds to the END (not overwrite) is FILE_APPEND.
file_put_contents($file, "Visit 1\n", ___);   // 👉 the append flag
file_put_contents($file, "Visit 2\n", ___);   // 👉 same flag again
file_put_contents($file, "Visit 3\n", ___);   // 👉 and again

// 2) Read the whole log back as one string.
echo ___;                                      // 👉 the "quick read" function: ___($file)

// ✅ Expected output:
//    Visit 1
//    Visit 2
//    Visit 3
?>

Visit 1
Visit 2
Visit 3

<?php
// JSON is the format APIs and config files speak. PHP converts between an
// array/object and a JSON string with one function each.
$file = sys_get_temp_dir() . "/config.json";

$settings = [
    "site"  => "My Blog",
    "admin" => "alice@example.com",
    "tags"  => ["php", "files", "json"],
];

// json_encode() turns the array into a JSON string. JSON_PRETTY_PRINT indents it
// so a human can read the file.
file_put_contents($file, json_encode($settings, JSON_PRETTY_PRINT));

// json_decode($s, true) turns the JSON string back into an associative array.
// (Without the 'true' you'd get an object instead.)
$loaded = json_decode(file_get_contents($file), true);
echo "Site:  " . $loaded["site"] . "\n";
echo "Tags:  " . implode(", ", $loaded["tags"]) . "\n";
?>

Site:  My Blog
Tags:  php, files, json

<?php
// 🎯 YOUR TURN — number every line of a file.
// Fill in the blanks so the loop reads one line at a time until the end.
$file = sys_get_temp_dir() . "/fruit.txt";
file_put_contents($file, "apple\nbanana\ncherry\n");

// 1) Open the file for READING (which one-letter mode is read-only?).
$handle = fopen($file, "___");                 // 👉 the read mode

$n = 1;
// 2) fgets() returns the next line, or false at the end. Loop while it is NOT false.
while (($line = ___($handle)) !== false) {     // 👉 the line-reading function
    echo $n . ": " . trim($line) . "\n";       // trim() drops the newline
    $n++;
}

// 3) Close the handle when you're done.
___($handle);                                   // 👉 the closing function

// ✅ Expected output:
//    1: apple
//    2: banana
//    3: cherry
?>

1: apple
2: banana
3: cherry

<?php
// Directories (folders) have their own small toolkit.
$dir = sys_get_temp_dir() . "/php_demo";

// mkdir() creates a folder. The 'true' makes it create missing parents too,
// and 0755 is the permission setting (owner can write, others can read/run).
if (!is_dir($dir)) {                       // is_dir() => does this folder exist?
    mkdir($dir, 0755, true);
}

// Put a couple of files inside so there's something to list.
file_put_contents("$dir/a.txt", "first");
file_put_contents("$dir/b.txt", "second");

// scandir() returns EVERY entry in the folder — including "." (here) and
// ".." (parent). Filter those two out before you use the list.
$entries = array_diff(scandir($dir), [".", ".."]);
echo "Files in folder:\n";
foreach ($entries as $name) {
    echo "  - $name\n";
}
?>

Files in folder:
  - a.txt
  - b.txt