String Functions

Introduction

Almost every real PHP program spends a lot of its time working with strings: cleaning up user input, formatting text for display, searching for a word inside a sentence, or breaking a comma-separated value into pieces. PHP ships with hundreds of built-in string functions, and a handful of them show up constantly.

This lesson walks through the string functions you will reach for the most: measuring length, changing case, trimming whitespace, replacing text, splitting and joining strings, extracting substrings, and searching inside a string — including the newer, more readable search functions added in PHP 8.

Measuring Length: strlen()

strlen() returns the number of characters (technically, bytes) in a string. It is one of the most frequently used string functions, often paired with validation logic like "password must be at least 8 characters."

<?php
$name = "PrograMinds";
$empty = "";

echo strlen($name) . "\n";
 echo strlen($empty) . "\n";

$password = "secret1";
if (strlen($password) < 8) {
    echo "Password is too short.\n";
}
?>

12
0
Password is too short.

Changing Case

strtoupper() converts a string to all uppercase, and strtolower() converts it to all lowercase. These are useful for case-insensitive comparisons and for formatting display text.

<?php
$city = "New Delhi";

echo strtoupper($city) . "\n";
echo strtolower($city) . "\n";

// Common use: case-insensitive comparison
$input = "YES";
if (strtolower($input) === "yes") {
    echo "Confirmed!\n";
}
?>

NEW DELHI
new delhi
Confirmed!

There are also ucfirst() (capitalizes only the first character) and ucwords() (capitalizes the first letter of every word) for title-style formatting.

<?php
$title = "the great gatsby";
echo ucfirst($title) . "\n";
echo ucwords($title) . "\n";
?>

The great gatsby
The Great Gatsby

Trimming Whitespace

User input often contains accidental leading or trailing spaces — someone hits the spacebar before typing an email address, or a form field is copy-pasted with extra whitespace. trim() removes whitespace (spaces, tabs, newlines) from both ends of a string; ltrim() removes it only from the left, and rtrim() only from the right.

<?php
$raw = "   hello@example.com   ";

echo "[" . trim($raw) . "]\n";
echo "[" . ltrim($raw) . "]\n";
echo "[" . rtrim($raw) . "]\n";
?>

[hello@example.com]
[hello@example.com   ]
[   hello@example.com]

Replacing Text: str_replace()

str_replace() searches a string for one or more values and replaces them with something else. It takes three arguments: what to search for, what to replace it with, and the string (or array of strings) to search inside.

<?php
$sentence = "PHP is fun. PHP is powerful.";
$updated = str_replace("PHP", "JavaScript", $sentence);
echo $updated . "\n";

// Replacing multiple values at once using arrays
$text = "I like cats and dogs.";
$result = str_replace(["cats", "dogs"], ["parrots", "rabbits"], $text);
echo $result . "\n";
?>

JavaScript is fun. JavaScript is powerful.
I like parrots and rabbits.

Splitting & Joining Strings

explode() breaks a string into an array of pieces based on a delimiter (a separator character or substring). implode() does the reverse — it joins an array of values back into a single string, placing a chosen separator between each element.

<?php
$csv = "apple,banana,cherry";
$fruits = explode(",", $csv);

print_r($fruits);
echo "First fruit: " . $fruits[0] . "\n";

$joined = implode(" | ", $fruits);
echo $joined . "\n";
?>

Array
(
    [0] => apple
    [1] => banana
    [2] => cherry
)
First fruit: apple
apple | banana | cherry

explode() is extremely common for parsing simple delimited data, such as splitting a full name into first and last name, or turning a comma-separated list of tags into an array.

<?php
$fullName = "Ravi Kumar";
$parts = explode(" ", $fullName);

echo "First name: " . $parts[0] . "\n";
echo "Last name: " . $parts[1] . "\n";
?>

First name: Ravi
Last name: Kumar

Extracting Substrings: substr()

substr() extracts a portion of a string, starting at a given position (0-based) for an optional number of characters. It is useful for previews, truncation, and pulling fixed-width fields out of a string.

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

echo substr($text, 7) . "\n";       // from position 7 to the end
echo substr($text, 7, 12) . "\n";   // 12 characters starting at position 7
echo substr($text, -9) . "\n";      // last 9 characters (negative start)
?>

PrograMinds!
PrograMinds
Journey!

Finding Text: strpos()

strpos() searches for the first occurrence of a substring inside a string and returns its numeric position, or false if it is not found. Because 0 is a valid (and falsy-looking) position, strpos() must always be compared using the strict === or !== operators, never == or !=.

<?php
$sentence = "Learning PHP is rewarding.";

$position = strpos($sentence, "PHP");
if ($position !== false) {
    echo "Found \"PHP\" at position $position.\n";
} else {
    echo "Not found.\n";
}

$missing = strpos($sentence, "Java");
var_dump($missing);
?>

Found "PHP" at position 9.
bool(false)

PHP 8 Search Helpers

PHP 8 introduced three small but very welcome functions that replace common strpos() patterns with clearer, purpose-built alternatives: str_contains(), str_starts_with(), and str_ends_with(). Each returns a plain true or false, so there is no confusing strict-comparison gotcha to remember.

<?php
$email = "amol@example.com";

var_dump(str_contains($email, "@example.com"));
var_dump(str_starts_with($email, "amol"));
var_dump(str_ends_with($email, ".com"));
var_dump(str_contains($email, "yahoo"));
?>

bool(true)
bool(true)
bool(true)
bool(false)

These functions read almost like plain English, which makes conditional logic involving text much easier to follow than an equivalent strpos() check.

<?php
$filename = "report.pdf";

if (str_ends_with($filename, ".pdf")) {
    echo "This is a PDF file.\n";
} else {
    echo "Unsupported file type.\n";
}
?>

This is a PDF file.

String Function Reference

Here is a quick-reference table of the string functions covered in this lesson, along with a few closely related ones you will encounter often.

Common Mistakes

Best Practices

Frequently Asked Questions

Key Takeaways

Summary

String functions are some of the most-used tools in everyday PHP code, whether you are cleaning up form input, formatting text for display, or parsing simple delimited data.

In this lesson, you learned how to measure, transform, search, split, and join strings using PHP's built-in functions, including the newer PHP 8 helpers that make common checks more readable. Next, you will look at how PHP handles numbers.