Working with Strings

A label maker lets you type text, fix a typo, make it all capitals, or trim it to fit. PHP's string functions are a label maker with a hundred buttons.

Websites are mostly text: names, messages, prices, addresses. PHP has a large set of built-in functions for working with it. A function is a named tool you call with parentheses, handing it values to work on, like strlen("Maria"). You'll write your own in Writing Functions; this lesson is about using PHP's.

One thing to know first: string functions don't change the original string. They give back a new one, which you can echo or store.

Length

strlen() counts the bytes in a string. For plain English letters, that's the same as the number of characters. But letters like ñ or é, and emoji, take more than one byte each, so for those, use mb_strlen(), which counts real characters (the mb stands for multibyte):

<?php
echo strlen("Maria"), "\n";
echo strlen("Niño"), "\n";
echo mb_strlen("Niño"), "\n";

5
5
4

When your text might include names from any language, reach for the mb_ version. Many string functions have one, like mb_strtoupper() and mb_substr().

Changing case

<?php
$title = "the little prince";
echo strtoupper($title), "\n";
echo ucfirst($title), "\n";
echo ucwords($title), "\n";
echo strtolower("SHOUTING"), "\n";

THE LITTLE PRINCE
The little prince
The Little Prince
shouting

ucfirst capitalizes the first letter, and ucwords the first letter of every word.

Trimming spaces

People often type extra spaces by accident, especially in forms. trim() removes spaces (and tabs and new lines) from both ends. ltrim() does only the left, and rtrim() only the right:

<?php
$typed = "   maria@example.com  ";
echo "[" . $typed . "]\n";
echo "[" . trim($typed) . "]\n";

[   maria@example.com  ]
[maria@example.com]

The square brackets are only there so you can see where the spaces are. Trimming user input is a habit worth building now.

Searching

<?php
$email = "maria@example.com";
var_dump(str_contains($email, "@"));
var_dump(str_starts_with($email, "maria"));
var_dump(str_ends_with($email, ".org"));
var_dump(strpos($email, "@"));

bool(true)
bool(true)
bool(false)
int(5)

• str_contains, str_starts_with, and str_ends_with answer yes-or-no questions. They're case-sensitive: "Maria" doesn't start with "maria".
• strpos gives the position where something first appears. Positions start counting at 0, so the @ in maria@... is at position 5.

strpos gives false when it finds nothing. Since 0 is a real position (the very start), always check its result with ===, not ==, as you learned in Operators and Expressions.

Cutting out a piece

substr($text, $start, $length) gives part of a string. Leave out the length to go to the end, and use a negative start to count from the end:

<?php
$code = "PH-2026-0042";
echo substr($code, 0, 2), "\n";
echo substr($code, 3, 4), "\n";
echo substr($code, -4), "\n";

PH
2026
0042

Replacing and repeating

<?php
echo str_replace("cats", "dogs", "I love cats. cats are great."), "\n";
echo str_repeat("=", 20), "\n";
echo str_pad("7", 3, "0", STR_PAD_LEFT), "\n";

I love dogs. dogs are great.
====================
007

• str_replace(find, replace, text) replaces every match.
• str_repeat repeats a string, handy for simple lines in the terminal.
• str_pad pads a string to a length. Here, it adds zeros on the left until it's 3 characters long.

Formatting numbers and text

number_format() makes numbers readable, with a thousands separator and a fixed number of decimals:

<?php
echo number_format(1234567.891), "\n";
echo number_format(1234567.891, 2), "\n";
echo number_format(0.5, 2), "\n";

1,234,568
1,234,567.89
0.50

For more control, sprintf() fills values into a pattern. Each % marks a spot: %s for a string, %d for a whole number, and %.2f for a decimal with 2 digits after the point. printf() does the same, but prints the result straight away:

<?php
$item = "Notebook";
$qty = 3;
$price = 45.5;
$line = sprintf("%s x%d = %.2f", $item, $qty, $qty * $price);
echo $line, "\n";
printf("%-10s|%5d|\n", "Pens", 12);

Notebook x3 = 136.50
Pens      |   12|

In the last line, %-10s means "a string, 10 characters wide, lined up on the left," and %5d means "a number, 5 characters wide," lined up on the right. That's perfect for tidy columns.

Long text: heredoc

For text that spans several lines, PHP has heredoc syntax. Start with <<< and a name you choose, write the text, and end with the same name on its own line. It works like a double-quoted string, so variables are filled in:

<?php
$name = "Maria";
$message = <<<TEXT
Dear $name,
Thank you for signing up.
See you on Saturday!
TEXT;
echo $message, "\n";

Dear Maria,
Thank you for signing up.
See you on Saturday!

Try it

A shop tidies up a product name and prints a price label. Predict each line exactly, including spaces.

Running PHP here

Running PHP right in the browser is coming to Syntaxia soon. For now, you can read and edit the code here. If you have PHP installed on your computer (see Setting Up), save it as index.php and run it with php index.php.

Check your prediction

[Rice Cooker]
11
HOME
bool(false)
Price: PHP 1,899.50
RICE COOKER (7 left)
-----------

trim runs first, removing the outer spaces, then ucwords capitalizes each word. "Rice Cooker" is 11 characters, including the space in the middle. str_contains is case-sensitive, and the SKU has RC, not rc, so it's false.

Try it yourself

1. Change the price to 25000. What does number_format($price, 2) print?
2. Use str_pad to print the number 42 as 00042.
3. Use mb_strtoupper on "señor", and compare it with strtoupper("señor"). Which one gets the ñ right?

Check your understanding

What does strpos("hello", "h") return?

1

true

false

0

Which function removes spaces from both ends of a string?

substr

trim

str_replace

strlen

Why use mb_strlen instead of strlen for a name like José?

mb_strlen is faster

strlen only works on numbers

strlen counts bytes, and é takes more than one byte

mb_strlen ignores spaces

Up next

You saw that 5 == "5" is true. PHP converts types behind the scenes more often than you might think, and sometimes the results are surprising. Find out when, and how to stay in control, in Type Juggling and Strict Comparisons.