PHP String Functions

Work with text in PHP: length, changing case, searching, replacing, trimming, splitting and joining, formatting with sprintf and number_format, and handling UTF-8 safely.

Lesson 3 of 86Beginner17 min read

Most of what a PHP website handles is text. Names and emails arrive from forms, product descriptions come from a database, and everything ends up as HTML sent to a browser. Cleaning, checking, shortening and formatting that text is a daily job for PHP developers.

PHP has a huge library of built-in string functions, more than almost any other language. You've already joined strings with . and put variables inside double quotes in the variables lesson. In this lesson you'll learn the functions you'll actually use most: measuring and changing text, searching and replacing, trimming spaces, splitting text into arrays and joining it back, and formatting numbers and prices neatly.

You'll also learn why a word like "café" can have a surprising length in PHP, and the simple mb_ functions that handle accented letters and other languages correctly.

Length, case and trimming

FunctionDoesExampleResult
strlen($s)Length in bytesstrlen("hello")5
strtoupper($s) / strtolower($s)Change casestrtoupper("php")PHP
ucfirst($s)Capitalise the first letterucfirst("london")London
ucwords($s)Capitalise every worducwords("ada lovelace")Ada Lovelace
trim($s)Remove spaces at both endstrim(" hi ")hi
str_repeat($s, n)Repeatstr_repeat("-", 5)-----

ltrim and rtrim remove spaces from only one side. Always trim() form input before checking or saving it: a name of three spaces isn't really a name.

Searching and replacing

  • str_contains($text, "php") returns true or false (PHP 8 and later).
  • str_starts_with() and str_ends_with() check the beginning or end, such as str_ends_with($file, ".pdf").
  • strpos($text, "php") gives the position of the first match, counting from 0, or false if it's missing.
  • str_replace("cat", "dog", $text) replaces every match. It also accepts arrays, to replace several words at once.
  • str_ireplace() and stripos() do the same while ignoring capital letters.

Be careful with strpos: a match at position 0 is a valid result, so always compare with === false, never with == false.

Parts of strings: substr, explode and implode

substr($s, start, length) takes part of a string: substr("Codevra", 0, 4) gives Code. A negative start counts from the end, so substr($file, -3) gives the last three characters.

explode(",", "red,green,blue") splits a string into an array, and implode(", ", $array) joins an array back into one string. Together they handle comma-separated values, tags, keywords and lists typed by users. To split on several possible separators, such as commas or spaces, you'll use preg_split from the regular expressions lesson.

Formatting with sprintf and number_format

sprintf builds a string from a template with placeholders, and printf prints it directly:

PHP
$line = sprintf("%s ordered %d items for £%.2f", "Sam", 3, 24.5);
// Sam ordered 3 items for £24.50

%s is a string, %d a whole number and %.2f a number with 2 decimals. %05d pads with zeros, and %-10s left-aligns in 10 characters.

number_format(1234567.891, 2) gives 1,234,567.89, the usual way to show prices and big numbers. str_pad("7", 3, "0", STR_PAD_LEFT) gives 007.

Heredoc and nowdoc for longer text

For several lines of text, such as an email body or an HTML snippet, PHP has heredoc syntax. It starts with <<< and a label, and ends with the same label on its own line:

PHP
$name = "Sam";
$count = 3;
echo <<<TXT
    Hello $name,
    You have {$count} new messages.
    TXT;

Heredoc interpolates variables like a double-quoted string, but you don't need to escape quotes inside it. The indentation of the closing label is removed from every line, so the output starts at Hello without leading spaces.

Nowdoc is the single-quoted version: write the label in quotes, <<<'RAW', and nothing inside is interpolated, so $price stays as literal text. It's handy for code samples and templates that contain dollar signs.

PHP Strings Syntax

String functions

strlen($s)  mb_strlen($s)  trim($s)
strtoupper($s)  strtolower($s)  ucfirst($s)  ucwords($s)
str_contains($s, "x")  str_starts_with($s, "x")  strpos($s, "x")
str_replace("old", "new", $s)
substr($s, 0, 10)
explode(",", $s)  implode(", ", $arr)
sprintf("%s: %.2f", $name, $price)
number_format($n, 2)  str_pad($s, 5, "0", STR_PAD_LEFT)

PHP Strings Summary

  • strlen, strtoupper, ucfirst, ucwords and trim measure and tidy text.
  • str_contains, str_starts_with and strpos search; check strpos with === false.
  • str_replace replaces text; substr takes part of a string.
  • explode splits a string into an array and implode joins an array into a string.
  • sprintf and number_format format values; use mb_ functions for UTF-8 text.

PHP Strings Examples

Each example shows the code, the output it produces and what each part does.

Example 1

Tidying form input

PHP
<?php
$name = "   ada LOVELACE ";
$email = "  Ada@Example.COM ";
$city = "new york";

$name = ucwords(strtolower(trim($name)));
$email = strtolower(trim($email));
$city = ucwords($city);

echo "Name: $name\n";
echo "Email: $email\n";
echo "City: $city\n";
echo "Name length: " . strlen($name) . "\n";
echo str_contains($email, "@example.com") ? "Company email\n" : "Personal email\n";
Output
Name: Ada Lovelace
Email: ada@example.com
City: New York
Name length: 12
Company email
Line-by-line explanation
  1. Line 6Functions work from the inside out: trim the spaces, lower-case everything, then capitalise each word.
  2. Line 7Emails are stored in lower case so "Ada@Example.COM" and "ada@example.com" match.
  3. Line 13strlen counts the characters of "Ada Lovelace", including the space.
  4. Line 14str_contains returns true or false, perfect for a ternary.
Example 2

Tags, previews and file names

PHP
<?php
$input = "php, web,  tutorial ,beginner";
$tags = array_map('trim', explode(",", $input));
echo "Tags: " . implode(" | ", $tags) . "\n";

$text = "PHP powers a huge share of the web, from blogs to online shops.";
$preview = strlen($text) > 30 ? substr($text, 0, 30) . "..." : $text;
echo $preview . "\n";

$file = "report-2024.PDF";
$isPdf = str_ends_with(strtolower($file), ".pdf");
echo $isPdf ? "PDF file\n" : "Other file\n";
echo "Position of 2024: " . strpos($file, "2024") . "\n";
Output
Tags: php | web | tutorial | beginner
PHP powers a huge share of the...
PDF file
Position of 2024: 7
Line-by-line explanation
  1. Line 3explode splits on commas, and array_map runs trim on every piece.
  2. Line 4implode joins the clean tags with a new separator.
  3. Line 7Only shorten text that's longer than 30 characters.
  4. Line 11Lower-case first, so ".PDF" and ".pdf" both count.
  5. Line 13"report-" is 7 characters, so 2024 starts at position 7.
Example 3

An invoice line with sprintf

PHP
<?php
$items = [
    ["Notebook", 3, 3.5],
    ["Backpack", 1, 34.99],
    ["Desk lamp", 2, 24.5],
];
$total = 0;
foreach ($items as [$name, $qty, $price]) {
    $line = $qty * $price;
    $total += $line;
    printf("%-10s x%-3d £%8s\n", $name, $qty, number_format($line, 2));
}
printf("%-15s £%8s\n", "TOTAL", number_format($total, 2));
echo "Invoice " . str_pad("42", 6, "0", STR_PAD_LEFT) . "\n";
Output
Notebook   x3   £   10.50
Backpack   x1   £   34.99
Desk lamp  x2   £   49.00
TOTAL           £   94.49
Invoice 000042
Line-by-line explanation
  1. Line 8Array destructuring in foreach gives each item's three values names.
  2. Line 11%-10s left-aligns the name in 10 characters, %-3d left-aligns the quantity, and %8s right-aligns the formatted price.
  3. Line 13The total line uses the same widths so the prices line up.
  4. Line 14str_pad adds zeros on the left until the string is 6 characters long.

Common PHP Strings Mistakes

Checking strpos with ==

Don't
if (strpos("php rocks", "php") == false) {
    echo "Not found";       // printed, because the position is 0
}
Do
if (strpos("php rocks", "php") === false) {
    echo "Not found";
}

Cutting accented text with substr

Don't
echo substr("Crème brûlée", 0, 3);       // "Cr" plus half a character
Do
echo mb_substr("Crème brûlée", 0, 3);    // "Crè"

Rounding prices with round() for display

Don't
echo "£" . round(12.5, 2);               // £12.5
Do
echo "£" . number_format(12.5, 2);       // £12.50

PHP Strings in Real Projects

Strings in PHP applications

Every form handler trims and validates input, blogs create short previews and URL slugs from titles, shops format prices with number_format, and invoices and emails are built with sprintf. Frameworks such as Laravel add helpers on top, like Str::slug() and Str::limit(), but they're built on the same functions you've learned here.

PHP Strings FAQ

What is the difference between strlen and mb_strlen?

strlen counts bytes, and mb_strlen counts characters. For plain English text they match, but strlen("café") is 5 while mb_strlen("café") is 4, because é uses two bytes in UTF-8. Use the mb_ functions whenever text may contain accented letters, other alphabets or emoji.

How do I check whether a string contains another string?

In PHP 8 and later, use str_contains($haystack, $needle), which returns true or false. It's case-sensitive; for a case-insensitive check, compare lowercase versions with mb_strtolower, or use stripos($haystack, $needle) !== false.

How do I reverse a string in PHP?

strrev("abc") gives "cba", but it reverses bytes, so it breaks accented letters and emoji. For UTF-8 text, split it into characters and join them backwards: implode('', array_reverse(mb_str_split($text))).

How do I convert a string to a number?

Cast it with (int) "42" or (float) "2.5", or use intval() and floatval(). Check the input first with is_numeric() or filter_var($value, FILTER_VALIDATE_INT), because casting quietly turns text such as "abc" into 0 and "12abc" into 12.

Should I use single or double quotes for strings?

Either is fine. Single quotes are literal and slightly simpler for text without variables; double quotes interpolate variables and understand escapes such as \n. Many teams use single quotes by default and double quotes when interpolation makes the code clearer. The speed difference is negligible.

PHP Strings Exercises

Answer each one and check it instantly. If you get stuck, open the hint before the answer.

Fill in the blankseasy

Complete the code so it removes spaces from both ends of the name.

$name = ("  Sam  ");
Predict the outputeasy

What does this print?

echo strtoupper("php") . strlen("code");
Predict the outputmedium

What does this print?

$parts = explode("-", "2024-07-05");
echo $parts[1];
Multiple choicemedium

Which line shows 1234.5 as 1,234.50?

Multiple choicehard

Why does strlen("café") return 5?

PHP Strings Quiz

5 questions to check what you learned.

  1. Which function joins array items into one string?

    • explode
    • implode
    • join_array
    • concat

  2. What does substr("Codevra", -3) return?

    • vra
    • Cod
    • dev
    • Codevr

  3. What does strpos return when the text isn't found?

    • -1
    • false
    • 0
    • null

  4. In sprintf("%.2f", 3.14159), what is the result?

    • 3.14159
    • 3.1
    • 3.14
    • 3

  5. Which function should you use to count the characters in user-entered text?

    • strlen
    • count
    • sizeof
    • mb_strlen

Related PHP topics

02Variables & StringsStore values in $variables, learn PHP's data types, and build text with concatenation and interpolation.06ArraysStore lists and labelled data in indexed and associative arrays, and use PHP's array functions.14Regular ExpressionsSearch, validate, extract and replace text by pattern with PHP's preg functions: delimiters, character classes, quantifiers, groups and flags.
Esc
↑↓ to navigateEnter to open