PHP String Functions

PHP provides over 100 built-in string functions for manipulating text. In this lesson, you'll learn the most essential functions that you'll use daily in PHP development!

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String Length

strlen() - Get String Length

<?php
$text = "Hello, World!";
echo strlen($text);  // Output: 13

// Useful for validation
$password = "abc123";
if (strlen($password) < 8) {
    echo "Password too short!";
}
?>

Case Conversion

<?php
$name = "john doe";
echo ucwords($name);  // Output: John Doe

// Case-insensitive comparison
$input = "HELLO";
if (strtolower($input) === "hello") {
    echo "Match!";
}
?>

Trimming Whitespace

<?php
$input = "  [email protected]  \n";
$clean = trim($input);  // "[email protected]"

// Trim specific characters
$url = "https://example.com/";
echo rtrim($url, '/');  // Remove trailing slash
?>

Substring Operations

substr() - Extract Part of String

<?php
$text = "Hello, World!";

// substr(string, start, length)
echo substr($text, 0, 5);   // "Hello"
echo substr($text, 7);      // "World!" (from position 7 to end)
echo substr($text, -6);     // "World!" (last 6 characters)
echo substr($text, 0, -7);  // "Hello," (all except last 7)
?>

str_split() - Split String into Array

<?php
$text = "Hello";
$chars = str_split($text);
print_r($chars);  // ["H", "e", "l", "l", "o"]

// Split into chunks
$chunks = str_split($text, 2);
print_r($chunks);  // ["He", "ll", "o"]
?>

Search and Replace

str_replace() - Replace All Occurrences

<?php
$text = "Hello World, Hello PHP!";

// Replace all "Hello" with "Hi"
$result = str_replace("Hello", "Hi", $text);
echo $result;  // "Hi World, Hi PHP!"

// Multiple replacements
$text = "I like apples and oranges";
$result = str_replace(
    ["apples", "oranges"],
    ["bananas", "grapes"],
    $text
);
echo $result;  // "I like bananas and grapes"

// Count replacements
$count = 0;
str_replace("Hello", "Hi", $text, $count);
echo $count;  // 2
?>

str_ireplace() - Case-Insensitive Replace

<?php
$text = "Hello HELLO hello";
$result = str_ireplace("hello", "Hi", $text);
echo $result;  // "Hi Hi Hi"
?>

Finding Substrings

<?php
$text = "Hello World";

// Find position
$pos = strpos($text, "World");
echo $pos;  // 6

// Check if substring exists
if (strpos($text, "World") !== false) {
    echo "Found!";
}

// Get substring from position
$result = strstr($text, "World");
echo $result;  // "World"
?>

String to Array Conversion

explode() - Split String by Delimiter

<?php
$csv = "John,Doe,30,Engineer";
$parts = explode(",", $csv);
print_r($parts);
// ["John", "Doe", "30", "Engineer"]

// Limit splits
$limited = explode(",", $csv, 2);
print_r($limited);
// ["John", "Doe,30,Engineer"]
?>

implode() - Join Array into String

<?php
$words = ["Hello", "World", "PHP"];
$sentence = implode(" ", $words);
echo $sentence;  // "Hello World PHP"

// Also called join()
$csv = join(",", $words);
echo $csv;  // "Hello,World,PHP"
?>

String Comparison

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

echo strcmp($str1, $str2);      // > 0 (different)
echo strcasecmp($str1, $str2);  // 0 (same, ignoring case)
?>

Other Useful Functions

str_repeat() - Repeat String

<?php
echo str_repeat("*", 10);  // "**********"
echo str_repeat("Ha", 3);  // "HaHaHa"
?>

str_pad() - Pad String

<?php
$num = "42";
echo str_pad($num, 5, "0", STR_PAD_LEFT);   // "00042"
echo str_pad($num, 5, "0", STR_PAD_RIGHT);  // "42000"
echo str_pad($num, 6, "-", STR_PAD_BOTH);   // "--42--"
?>

str_word_count() - Count Words

<?php
$text = "Hello World PHP";
echo str_word_count($text);  // 3

// Get array of words
$words = str_word_count($text, 1);
print_r($words);  // ["Hello", "World", "PHP"]
?>

strrev() - Reverse String

<?php
echo strrev("Hello");  // "olleH"
?>

Common Mistakes

<?php
$text = "Hello World";

if (strpos($text, "Hello") == false) {  // ❌ Wrong!
    // This executes because strpos returns 0 (position)
    // and 0 == false is true
}

if (strpos($text, "Hello") === false) {  // ✅ Correct
    // This won't execute
}
?>

<?php
$text = "Hello World";

// Wrong parameter order
substr($text, 5, 0);  // ❌ Empty string

// Correct
substr($text, 0, 5);  // ✅ "Hello"
?>

Summary

What's Next?

You've mastered strings! Now let's learn about Constants - values that never change throughout your program's execution. Perfect for configuration values, API keys, and more!