PHP String Functions - Complete Reference

Introduction to PHP String Functions

PHP provides a rich set of built-in string functions for manipulating, searching, formatting, and validating strings. This reference covers the most commonly used string functions with practical examples.

String Length and Information

strlen() - Get String Length

<?php
$text = "Hello World";
echo strlen($text); // Output: 11

$unicode = "Hello 世界";
echo strlen($unicode); // Output: 12 (bytes, not characters)
echo mb_strlen($unicode, 'UTF-8'); // Output: 8 (characters)

// Check if string is empty
function isEmptyString($str) {
    return strlen(trim($str)) === 0;
}

echo isEmptyString("   ") ? "Empty" : "Not empty"; // Output: Empty
?>

str_word_count() - Count Words

<?php
$text = "The quick brown fox jumps over the lazy dog";

// Count words
echo str_word_count($text); // Output: 9

// Get array of words
$words = str_word_count($text, 1);
print_r($words);
/* Output:
Array (
    [0] => The
    [1] => quick
    [2] => brown
    [3] => fox
    [4] => jumps
    [5] => over
    [6] => the
    [7] => lazy
    [8] => dog
)
*/

// Get word positions
$positions = str_word_count($text, 2);
print_r($positions);
/* Output:
Array (
    [0] => The
    [4] => quick
    [10] => brown
    [16] => fox
    [20] => jumps
    [26] => over
    [31] => the
    [35] => lazy
    [40] => dog
)
*/
?>

String Searching and Finding

strpos() - Find Position of Substring

<?php
$haystack = "The quick brown fox jumps over the lazy dog";
$needle = "brown";

$position = strpos($haystack, $needle);
if ($position !== false) {
    echo "Found '$needle' at position $position"; // Output: Found 'brown' at position 10
} else {
    echo "'$needle' not found";
}

// Case-insensitive search
$position = stripos($haystack, "BROWN");
echo $position; // Output: 10

// Find last occurrence
$position = strrpos($haystack, "the");
echo $position; // Output: 31

// Find first occurrence of any character from a set
$position = strpbrk($haystack, "aeiou");
echo $position; // Output: e quick brown fox jumps over the lazy dog
?>

str_contains() - Check if String Contains Substring (PHP 8+)

<?php
$text = "The quick brown fox";

if (str_contains($text, "brown")) {
    echo "Contains 'brown'"; // Output: Contains 'brown'
}

if (str_starts_with($text, "The")) {
    echo "Starts with 'The'"; // Output: Starts with 'The'
}

if (str_ends_with($text, "fox")) {
    echo "Ends with 'fox'"; // Output: Ends with 'fox'
}

// For older PHP versions
function contains($haystack, $needle) {
    return strpos($haystack, $needle) !== false;
}

function startsWith($haystack, $needle) {
    return strpos($haystack, $needle) === 0;
}

function endsWith($haystack, $needle) {
    return substr($haystack, -strlen($needle)) === $needle;
}
?>

String Manipulation

substr() - Extract Substring

<?php
$text = "Hello World";

// Extract from position 6
echo substr($text, 6); // Output: World

// Extract 5 characters from position 0
echo substr($text, 0, 5); // Output: Hello

// Extract from end
echo substr($text, -5); // Output: World

// Extract from position with negative length
echo substr($text, 0, -6); // Output: Hello

// Safe substring function
function safeSubstr($string, $start, $length = null) {
    if ($start < 0) {
        $start = max(0, strlen($string) + $start);
    }
    
    if ($length === null) {
        return substr($string, $start);
    }
    
    return substr($string, $start, $length);
}

echo safeSubstr("Hello", 10); // Output: (empty string)
?>

str_replace() - Replace Substrings

<?php
$text = "The quick brown fox jumps over the lazy dog";

// Simple replacement
$newText = str_replace("fox", "cat", $text);
echo $newText; // Output: The quick brown cat jumps over the lazy dog

// Multiple replacements
$search = ["quick", "brown", "lazy"];
$replace = ["slow", "red", "active"];
$newText = str_replace($search, $replace, $text);
echo $newText; // Output: The slow red fox jumps over the active dog

// Case-insensitive replacement
$newText = str_ireplace("QUICK", "slow", $text);
echo $newText; // Output: The slow brown fox jumps over the lazy dog

// Count replacements
$count = 0;
$newText = str_replace("the", "a", $text, $count);
echo "Replaced $count occurrences"; // Output: Replaced 2 occurrences

// Advanced replacement function
function replaceWords($text, $replacements) {
    $pattern = '/\b(' . implode('|', array_keys($replacements)) . ')\b/i';
    return preg_replace_callback($pattern, function($matches) use ($replacements) {
        $word = strtolower($matches[1]);
        return $replacements[$word] ?? $matches[1];
    }, $text);
}

$replacements = [
    'quick' => 'fast',
    'brown' => 'red',
    'fox' => 'cat'
];
echo replaceWords($text, $replacements);
?>

trim() - Remove Whitespace

<?php
$text = "  Hello World  ";

// Remove whitespace from both ends
echo "'" . trim($text) . "'"; // Output: 'Hello World'

// Remove from left only
echo "'" . ltrim($text) . "'"; // Output: 'Hello World  '

// Remove from right only
echo "'" . rtrim($text) . "'"; // Output: '  Hello World'

// Remove specific characters
$text = "...Hello World...";
echo trim($text, '.'); // Output: Hello World

// Remove multiple characters
$text = " \t\n Hello World \t\n ";
echo "'" . trim($text) . "'"; // Output: 'Hello World'

// Custom trim function
function smartTrim($string, $chars = " \t\n\r\0\x0B") {
    return trim($string, $chars);
}

// Remove quotes
$quoted = '"Hello World"';
echo trim($quoted, '"'); // Output: Hello World
?>

Case Conversion

strtoupper() / strtolower() - Change Case

<?php
$text = "Hello World";

// Convert to uppercase
echo strtoupper($text); // Output: HELLO WORLD

// Convert to lowercase
echo strtolower($text); // Output: hello world

// Capitalize first letter
echo ucfirst($text); // Output: Hello World

// Capitalize first letter of each word
echo ucwords($text); // Output: Hello World

// Capitalize words with custom delimiters
echo ucwords("hello-world", "-"); // Output: Hello-World

// Custom title case function
function titleCase($string) {
    $smallWords = ['a', 'an', 'and', 'as', 'at', 'but', 'by', 'for', 'if', 'in', 'of', 'on', 'or', 'the', 'to', 'up'];
    
    $words = explode(' ', strtolower($string));
    
    foreach ($words as $key => $word) {
        if ($key === 0 || $key === count($words) - 1 || !in_array($word, $smallWords)) {
            $words[$key] = ucfirst($word);
        }
    }
    
    return implode(' ', $words);
}

echo titleCase("the quick brown fox"); // Output: The Quick Brown Fox

// Multibyte case conversion (for Unicode)
$unicode = "héllo wörld";
echo mb_strtoupper($unicode); // Output: HÉLLO WÖRLD
echo mb_strtolower($unicode); // Output: héllo wörld
?>

String Splitting and Joining

explode() / implode() - Split and Join

<?php
// Split string into array
$text = "apple,banana,orange,grape";
$fruits = explode(",", $text);
print_r($fruits);
/* Output:
Array (
    [0] => apple
    [1] => banana
    [2] => orange
    [3] => grape
)
*/

// Limit splits
$fruits = explode(",", $text, 2);
print_r($fruits);
/* Output:
Array (
    [0] => apple
    [1] => banana,orange,grape
)
*/

// Join array into string
$fruits = ["apple", "banana", "orange"];
echo implode(", ", $fruits); // Output: apple, banana, orange

// Alternative: join() is alias of implode()
echo join(" | ", $fruits); // Output: apple | banana | orange

// Split by multiple delimiters
function multiExplode($delimiters, $string) {
    $pattern = '/[' . preg_quote(implode('', $delimiters), '/') . ']/';
    return preg_split($pattern, $string);
}

$text = "apple,banana;orange|grape";
$fruits = multiExplode([',', ';', '|'], $text);
print_r($fruits);

// Smart CSV parsing
function parseCSV($line, $delimiter = ',', $enclosure = '"') {
    $fields = [];
    $field = '';
    $inEnclosure = false;
    $len = strlen($line);
    
    for ($i = 0; $i < $len; $i++) {
        $char = $line[$i];
        
        if ($char === $enclosure) {
            $inEnclosure = !$inEnclosure;
        } elseif ($char === $delimiter && !$inEnclosure) {
            $fields[] = $field;
            $field = '';
        } else {
            $field .= $char;
        }
    }
    
    $fields[] = $field;
    return $fields;
}

$csvLine = '"John Doe","25","New York, NY"';
$fields = parseCSV($csvLine);
print_r($fields);
?>

String Padding and Alignment

str_pad() - Pad String

<?php
$text = "Hello";

// Pad to 10 characters (right padding)
echo str_pad($text, 10); // Output: "Hello     "

// Pad to 10 characters (left padding)
echo str_pad($text, 10, " ", STR_PAD_LEFT); // Output: "     Hello"

// Pad to 10 characters (both sides)
echo str_pad($text, 10, " ", STR_PAD_BOTH); // Output: "  Hello   "

// Pad with custom character
echo str_pad($text, 10, "*", STR_PAD_LEFT); // Output: "*****Hello"

// Pad with multiple characters
echo str_pad($text, 15, ".-", STR_PAD_BOTH); // Output: ".-.-Hello.-.-."

// Number padding
function padNumber($number, $length = 3) {
    return str_pad($number, $length, "0", STR_PAD_LEFT);
}

echo padNumber(5); // Output: 005
echo padNumber(42); // Output: 042
echo padNumber(123); // Output: 123

// Format price
function formatPrice($price) {
    return '$' . number_format($price, 2);
}

echo formatPrice(1234.5); // Output: $1,234.50
?>

String Formatting

sprintf() - Format String

<?php
// Basic formatting
$name = "John";
$age = 25;
echo sprintf("My name is %s and I am %d years old", $name, $age);
// Output: My name is John and I am 25 years old

// Number formatting
$price = 1234.567;
echo sprintf("Price: $%.2f", $price); // Output: Price: $1234.57

// Padding with sprintf
echo sprintf("%05d", 42); // Output: 00042
echo sprintf("%-10s", "Hello"); // Output: "Hello     "

// Multiple values
echo sprintf("%s costs $%.2f and weighs %.1f kg", "Apple", 0.5, 0.2);
// Output: Apple costs $0.50 and weighs 0.2 kg

// Date formatting
$date = new DateTime();
echo sprintf("Today is %s", $date->format('Y-m-d')); // Output: Today is 2023-01-01

// Custom formatting function
function formatBytes($size, $precision = 2) {
    $units = ['B', 'KB', 'MB', 'GB', 'TB'];
    
    for ($i = 0; $size >= 1024 && $i < count($units) - 1; $i++) {
        $size /= 1024;
    }
    
    return sprintf("%.{$precision}f %s", $size, $units[$i]);
}

echo formatBytes(1536); // Output: 1.50 KB
echo formatBytes(1048576); // Output: 1.00 MB

// Template system
function simpleTemplate($template, $vars) {
    return preg_replace_callback('/\{(\w+)\}/', function($matches) use ($vars) {
        return $vars[$matches[1]] ?? $matches[0];
    }, $template);
}

$template = "Hello {name}, you have {count} messages.";
$vars = ['name' => 'John', 'count' => 5];
echo simpleTemplate($template, $vars); // Output: Hello John, you have 5 messages.
?>

String Comparison

strcmp() - Compare Strings

<?php
$str1 = "apple";
$str2 = "banana";

// Binary safe string comparison
$result = strcmp($str1, $str2);
echo $result; // Output: negative number (apple < banana)

// Case-insensitive comparison
$result = strcasecmp("Apple", "APPLE");
echo $result; // Output: 0 (equal)

// Natural order comparison
$files = ["file1.txt", "file10.txt", "file2.txt"];
usort($files, 'strnatcmp');
print_r($files); // Output: file1.txt, file2.txt, file10.txt

// Version comparison
echo version_compare("1.2.3", "1.2.4"); // Output: -1

// Levenshtein distance (edit distance)
$word1 = "kitten";
$word2 = "sitting";
echo levenshtein($word1, $word2); // Output: 3

// Similar text percentage
$text1 = "Hello World";
$text2 = "Hello Word";
similar_text($text1, $text2, $percent);
echo "Similarity: " . round($percent, 2) . "%"; // Output: Similarity: 90.91%

// Soundex comparison (phonetic similarity)
echo soundex("Smith"); // Output: S530
echo soundex("Smyth"); // Output: S530

function isSimilarSounding($word1, $word2) {
    return soundex($word1) === soundex($word2);
}

echo isSimilarSounding("Smith", "Smyth") ? "Similar" : "Different"; // Output: Similar
?>

String Validation

Validation Functions

<?php
// Email validation
function isValidEmail($email) {
    return filter_var($email, FILTER_VALIDATE_EMAIL) !== false;
}

echo isValidEmail("[email protected]") ? "Valid" : "Invalid"; // Output: Valid

// URL validation
function isValidURL($url) {
    return filter_var($url, FILTER_VALIDATE_URL) !== false;
}

echo isValidURL("https://example.com") ? "Valid" : "Invalid"; // Output: Valid

// Check if string is numeric
function isNumericString($str) {
    return is_numeric($str);
}

echo isNumericString("123.45") ? "Numeric" : "Not numeric"; // Output: Numeric

// Check if string contains only alphabetic characters
function isAlpha($str) {
    return ctype_alpha($str);
}

echo isAlpha("HelloWorld") ? "Alphabetic" : "Not alphabetic"; // Output: Alphabetic

// Check if string contains only alphanumeric characters
function isAlphanumeric($str) {
    return ctype_alnum($str);
}

echo isAlphanumeric("Hello123") ? "Alphanumeric" : "Not alphanumeric"; // Output: Alphanumeric

// Custom validation function
function validatePassword($password) {
    $errors = [];
    
    if (strlen($password) < 8) {
        $errors[] = "Password must be at least 8 characters long";
    }
    
    if (!preg_match('/[A-Z]/', $password)) {
        $errors[] = "Password must contain at least one uppercase letter";
    }
    
    if (!preg_match('/[a-z]/', $password)) {
        $errors[] = "Password must contain at least one lowercase letter";
    }
    
    if (!preg_match('/[0-9]/', $password)) {
        $errors[] = "Password must contain at least one number";
    }
    
    if (!preg_match('/[^A-Za-z0-9]/', $password)) {
        $errors[] = "Password must contain at least one special character";
    }
    
    return empty($errors) ? true : $errors;
}

$result = validatePassword("MyPass123!");
echo is_array($result) ? implode(", ", $result) : "Valid password";
?>

Advanced String Operations

String Encoding and Escaping

<?php
// HTML encoding
$text = "<script>alert('XSS')</script>";
echo htmlspecialchars($text); // Output: &lt;script&gt;alert('XSS')&lt;/script&gt;

// URL encoding
$text = "Hello World!";
echo urlencode($text); // Output: Hello+World%21
echo rawurlencode($text); // Output: Hello%20World%21

// Base64 encoding
$text = "Hello World";
$encoded = base64_encode($text);
echo $encoded; // Output: SGVsbG8gV29ybGQ=
echo base64_decode($encoded); // Output: Hello World

// JSON encoding
$data = ["name" => "John", "age" => 30];
echo json_encode($data); // Output: {"name":"John","age":30}

// Escape for SQL (basic example - use prepared statements in practice)
function escapeSql($string) {
    return str_replace("'", "''", $string);
}

// Escape for shell command
$command = "echo " . escapeshellarg($text);

// Remove HTML tags
$html = "<p>This is <strong>bold</strong> text</p>";
echo strip_tags($html); // Output: This is bold text
echo strip_tags($html, '<strong>'); // Output: This is <strong>bold</strong> text

// Convert special characters
$text = "café naïve résumé";
echo htmlentities($text, ENT_QUOTES, 'UTF-8'); 
// Output: caf&eacute; na&iuml;ve r&eacute;sum&eacute;
?>

String Hashing and Checksums

<?php
$text = "Hello World";

// MD5 hash
echo md5($text); // Output: b10a8db164e0754105b7a99be72e3fe5

// SHA1 hash
echo sha1($text); // Output: 0a4d55a8d778e5022fab701977c5d840bbc486d0

// SHA256 hash
echo hash('sha256', $text);

// Password hashing (secure)
$password = "mypassword";
$hash = password_hash($password, PASSWORD_DEFAULT);
echo $hash;

// Verify password
$isValid = password_verify($password, $hash);
echo $isValid ? "Valid" : "Invalid";

// CRC32 checksum
echo crc32($text); // Output: 222957957

// Custom hash function for short IDs
function generateShortId($input, $length = 8) {
    return substr(base_convert(md5($input), 16, 36), 0, $length);
}

echo generateShortId("Hello World"); // Output: 9ql8xmqm
?>

This comprehensive reference covers the most essential PHP string functions with practical examples for real-world development scenarios.

String Functions Reference

Introduction to PHP String Functions

String Length and Information

strlen() - Get String Length

str_word_count() - Count Words

String Searching and Finding

strpos() - Find Position of Substring

str_contains() - Check if String Contains Substring (PHP 8+)

String Manipulation

substr() - Extract Substring

str_replace() - Replace Substrings

trim() - Remove Whitespace

Case Conversion

strtoupper() / strtolower() - Change Case

String Splitting and Joining

explode() / implode() - Split and Join

String Padding and Alignment

str_pad() - Pad String

String Formatting

sprintf() - Format String

String Comparison

strcmp() - Compare Strings

String Validation

Validation Functions

Advanced String Operations

String Encoding and Escaping

String Hashing and Checksums

On this page

Introduction to PHP String Functions

String Length and Information

String Searching and Finding

String Manipulation

Case Conversion

String Splitting and Joining

String Padding and Alignment

String Formatting

String Comparison

String Validation

Advanced String Operations