Practical PHP Notes: Commonly Used Syntax and Functions I Use in Real Projects
I’ve been writing PHP for many years now, and honestly, I’m not the kind of developer who memorizes syntax every day. Instead, whenever a certain feature shows up repeatedly in real projects, I make sure I truly understand it, double-check the details, and fine-tune how I use it.
This article is essentially my personal cheat sheet—a collection of PHP functions I use and look up most often when building systems, writing APIs, or integrating external services. I’m putting it all in one place mainly for myself, but hopefully it’ll be useful to you as well.
String Handling
// Extract substrings
substr($string, $offset, $length);
mb_substr($string, $offset, $length, 'UTF-8');
// Replace strings
str_replace($search, $replace, $string);
// Handle string length
strlen($string);
mb_strlen($string, 'UTF-8');
// Trim whitespace
trim($string)
// Check if a string contains a keyword
str_contains($string, 'keyword');
// Check prefix / suffix
str_starts_with($string, 'keyword');
str_ends_with($string, 'keyword');
// Case conversion
strtolower($string) // Convert to lowercase
strtoupper($string) // Convert to uppercase
ucfirst($string) // Uppercase the first character
// Split and join strings
explode(',', $string);
implode(',', $array);
JSON
// Convert an array to JSON
// JSON_UNESCAPED_UNICODE: keep Unicode characters readable
// JSON_UNESCAPED_SLASHES: keep URLs readable
// JSON_PRETTY_PRINT: formatted output
json_encode($data, JSON_UNESCAPED_UNICODE | JSON_PRETTY_PRINT);
// Decode JSON back into an array
$array = json_decode($json, true);
// Check if json_decode failed
if ($array === null && json_last_error() !== JSON_ERROR_NONE) {
// Invalid JSON
}
File Handling
Writing Files
// Write a file
file_put_contents(
'data.json',
json_encode($data, JSON_UNESCAPED_UNICODE | JSON_PRETTY_PRINT)
);
// Append to a file
// FILE_APPEND: append mode
// LOCK_EX: prevent race conditions
file_put_contents(
'app.log',
"[" . date('Y-m-d H:i:s') . "] something happened\n",
FILE_APPEND | LOCK_EX
);
// Write a CSV file
$fp = fopen('data.csv', 'w');
fwrite($fp, chr(0xEF) . chr(0xBB) . chr(0xBF)); // UTF-8 BOM
fputcsv($fp, ['id', 'name', 'score']);
fputcsv($fp, [1, 'Mark', 95]);
fputcsv($fp, [2, 'Alex', 88]);
fclose($fp);
Reading Files
// Read entire file
$content = file_get_contents('data.json');
// Read line by line (method 1)
$lines = file('data.txt', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
foreach ($lines as $line) {
echo $line;
}
// Read line by line (method 2 – better for large files)
$fp = fopen('data.txt', 'r');
while (($line = fgets($fp)) !== false) {
echo $line;
}
fclose($fp);
// Read CSV into an associative array
$fp = fopen('data.csv', 'r');
$header = fgetcsv($fp); // First row is the header
$data = [];
while (($row = fgetcsv($fp)) !== false) {
$data[] = array_combine($header, $row);
}
fclose($fp);
Working with Timestamps
Basics
According to Wikipedia, a Unix timestamp is the number of seconds since January 1, 1970, 00:00:00 UTC.
If you want to add time, you can simply add seconds—or use strtotime, which is surprisingly powerful. PHP can parse almost any English time description into a Unix timestamp. Just remember: PHP always uses the server’s time and timezone, so make sure those are configured correctly.
// Convert time descriptions to timestamps
time(); // Current timestamp
strtotime('now'); // Current timestamp
strtotime('2020-10-28 12:50:21'); // Specific datetime
strtotime('2020-10-28 14:00:00 +1 day'); // Add time
// Convert timestamps to formatted strings
date('Y-m-d H:i:s', time());
date('Y-m-d H:i:s', strtotime('2020-10-28 12:50:21'));
Modern Date/Time Handling (Recommended)
// Create DateTime objects
$dt = new DateTime('now', new DateTimeZone('Asia/Taipei'));
$dt = new DateTime('2025-01-10 08:30:00', new DateTimeZone('Asia/Taipei'));
// Create DateTime using a specific format
$dt = DateTime::createFromFormat(
'Y-m-d H:i:s',
'2025-01-10 08:30:00',
new DateTimeZone('Asia/Taipei')
);
// Format output
echo $dt->format('Y/m/d H:i:s');
// Add / subtract time
$dt = $dt->add(new DateInterval('P1D'));
$dt = $dt->sub(new DateInterval('P1D'));
// Date Difference
$dt1 = new DateTimeImmutable(
'2025-01-01 08:30:00',
new DateTimeZone('Asia/Taipei')
);
$dt2 = new DateTimeImmutable(
'2025-01-03 11:45:20',
new DateTimeZone('Asia/Taipei')
);
$interval = $dt2->diff($dt1);
$interval->y; // Years
$interval->m; // Months
$interval->d; // Days (excluding years/months)
$interval->h; // Hours
$interval->i; // Minutes
$interval->s; // Seconds
$interval->days; // Total days difference
echo $interval->format('%a days %h hours %i minutes %s seconds');
Date Comparison
if ($dt1 < $dt2) {
}
Notes
DateInterval string examples
- P1Y2M3DT4H5M6S: 1 year, 2 months, 3 days, 4 hours, 5 minutes, 6 seconds
- P3DT6S: 3 days, 6 seconds
- P3DT5M6S: 3 days, 5 minutes, 6 seconds
If there’s any time component, you must include T.
DateTime vs DateTimeImmutable
- DateTime is mutable — modifying it changes the original object
- DateTimeImmutable is immutable — modifications return a new object
Both implement DateTimeInterface, so you can safely compare them. Comparisons are based on actual time, not object identity.
Calling APIs with cURL
GET Example
$params = [
'foo1' => 'bar1',
'foo2' => 'bar2',
'foo3' => 'bar3',
];
$queryString = http_build_query($params);
// cURL
$curl = curl_init();
curl_setopt($curl, CURLOPT_URL, URL . '?' . $queryString);
curl_setopt($curl, CURLOPT_TIMEOUT, 60);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_HTTPHEADER, [
'Authorization: Bearer ' . $token,
'Accept: application/json',
]);
$response = curl_exec($curl);
POST Example
$curl = curl_init();
curl_setopt($curl, CURLOPT_URL, URL);
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_POSTFIELDS, [
'foo1' => 'bar1',
'foo2' => 'bar2',
'foo3' => 'bar3',
// Single file upload
'file' => new CURLFile($inputPath, mime_content_type($inputPath), basename($inputPath)),
]);
curl_setopt($curl, CURLOPT_TIMEOUT, 60);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_HTTPHEADER, [
'Authorization: Bearer ' . $token,
'Accept: application/json',
]);
$response = curl_exec($curl);
For uploading multiple files with cURL, please refer to the separate article for a detailed explanation.
Handling the Response
$response = curl_exec($curl);
// cURL execution error
if ($response === false) {
$errno = curl_errno($curl);
$errmsg = curl_error($curl);
throw new Exception('cURL Error ' . $errno . ': ' . $errmsg);
}
// Check HTTP status code
$httpCode = curl_getinfo($curl, CURLINFO_HTTP_CODE);
if ($httpCode < 200 || $httpCode >= 300) {
throw new Exception("HTTP {$httpCode}: {$response}");
}
// Decode JSON response
$data = json_decode($response, true);
if ($data === null && json_last_error() !== JSON_ERROR_NONE) {
throw new Exception('JSON decode error: ' . json_last_error_msg());
}
curl_close($curl);
Retrieving Headers
Request Headers
$curl = curl_init();
curl_setopt($curl, CURLOPT_URL, URL);
curl_setopt($curl, CURLINFO_HEADER_OUT, true);
$response = curl_exec($ch);
$requestHeader = curl_getinfo($ch, CURLINFO_HEADER_OUT);
Response Headers
$curl = curl_init();
curl_setopt($curl, CURLOPT_URL, URL);
curl_setopt($curl, CURLOPT_HEADER, true);
$response = curl_exec($curl);
$headerSize = curl_getinfo($ch, CURLINFO_HEADER_SIZE);
$header = substr($response, 0, $headerSize);
$body = substr($response, $headerSize);
Commonly Used curl_setopt() Options
| Option | Description |
|---|---|
| CURLOPT_VERBOSE | Debug mode |
| CURLOPT_URL | Target URL |
| CURLOPT_CONNECTTIMEOUT | Max time to wait for connection |
| CURLOPT_TIMEOUT | Max total request time |
| CURLOPT_HEADER | Include response headers |
| CURLINFO_HEADER_OUT | Retrieve outgoing request headers |
| CURLOPT_HTTPHEADER | Set HTTP headers (don’t manually set Content-Type) |
| CURLOPT_RETURNTRANSFER | Return response as a string |
| CURLOPT_POST | Enable POST |
| CURLOPT_POSTFIELDS | POST data |
| CURLOPT_CUSTOMREQUEST | PUT, DELETE, PATCH, OPTIONS |
| CURLOPT_SSL_VERIFYPEER | Verify SSL certificate |
| CURLOPT_SSL_VERIFYHOST | Verify SSL host |
Downloading Files
$url = 'https://example.com/image.jpg';
$savePath = __DIR__ . '/download/image.jpg';
// Ensure directory exists
if (!is_dir(dirname($savePath))) {
mkdir(dirname($savePath), 0755, true);
}
// cURL
$fp = fopen($savePath, 'w');
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_FILE, $fp);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
curl_setopt($ch, CURLOPT_TIMEOUT, 60);
curl_exec($ch);
if (curl_errno($ch)) {
throw new Exception(curl_error($ch));
}
curl_close($ch);
fclose($fp);