PHP Strings: Quotes, Concatenation and Interpolation

A PHP string is text in single or double quotes. Join strings with the dot operator, $first . ' ' . $last, or put a variable straight into double quotes: "Hello, $name".

<?php
$first = "Ada";
$last = "Lovelace";

// Concatenation with the dot operator
$full = $first . " " . $last;
echo $full . "\n";

// Interpolation: the variable goes inside double quotes
echo "Hello, $first\n";
echo "Your name has " . strlen($full) . " characters\n";

The dot joins any two values into a new string. Numbers are converted for you, so "Total: " . 42 is "Total: 42".

Single vs double quotes

Double quotes do two extra things: they replace variables with their values, and they turn escape sequences such as \n (newline) and \t (tab) into the characters they stand for. Single quotes print the text exactly as written, except \' and \\.

<?php
$name = "Ada";

echo "Hello, $name\n";
echo 'Hello, $name\n';
echo "\n";

echo 'It\'s a single-quoted string' . "\n";
echo "Tab:\t|\n";
echo 'Tab:\t|' . "\n";

Use single quotes for fixed text and double quotes when you want a variable or a \n inside. The speed difference between them is too small to measure, so pick whichever makes the line easier to read.

Concatenate strings with . and .=

.= appends to the end of a string variable. It is the usual way to build up text in a loop, for example a piece of HTML. Run this block and the editor opens the Page tab, which shows the list rendered.

<?php
$fruits = ["Apple", "Banana", "Cherry"];

$html = "<ul>";
foreach ($fruits as $fruit) {
    $html .= "<li>" . $fruit . "</li>";
}
$html .= "</ul>";

echo "<p>We have " . count($fruits) . " fruits:</p>";
echo $html;

Precedence matters when you mix . with arithmetic. Since PHP 8, + and - bind tighter than ., so "Sum: " . 2 + 3 is "Sum: 5". Parentheses make it obvious to the next reader: "Sum: " . (2 + 3).

Put variables, arrays and objects inside a string

A plain variable works on its own inside double quotes. For an array element, an object property chain or a method call, wrap the expression in curly braces. The braces also separate a variable from letters that follow it.

<?php
$user = ["name" => "Grace", "city" => "Arlington"];
$count = 3;
$fruit = "apple";

echo "Name: {$user['name']}\n";
echo "City: $user[city]\n";
echo "I ate {$count} {$fruit}s\n";

$date = new DateTime("2026-03-14");
echo "Pi day: {$date->format('F j')}\n";

// A plain function is not called inside a string
echo "{strtoupper($fruit)}\n";

Methods work inside the braces, plain functions do not: the last line prints the braces and the function name around the value of $fruit. Call the function before the string, or use sprintf when the string has many values.

Change case: strtoupper, strtolower, ucfirst, ucwords

<?php
$title = "the quick brown fox";

echo strtoupper($title) . "\n";
echo strtolower("HeLLo WoRLD") . "\n";
echo ucfirst($title) . "\n";
echo ucwords($title) . "\n";
echo lcfirst("Hello") . "\n";

// ucwords with your own word separators
echo ucwords("mary-jane o'neil", " -'") . "\n";

These functions work byte by byte and only change the letters a to z. For text with accents, Cyrillic or Greek, use the multibyte versions, which understand UTF-8:

<?php
$word = "élan";

echo strtoupper($word) . "\n";
echo mb_strtoupper($word) . "\n";
echo mb_convert_case("ΑΘΉΝΑ city", MB_CASE_TITLE) . "\n";

Read single characters and repeat strings

A string can be indexed like an array. Negative offsets count from the end. For counting characters see strlen.

<?php
$word = "PHP strings";

echo $word[0] . "\n";
echo $word[-1] . "\n";
echo substr($word, 4) . "\n";

echo str_repeat("=", 20) . "\n";
echo str_pad("7", 3, "0", STR_PAD_LEFT) . "\n";

Common mistake: + instead of .

In JavaScript + joins strings. In PHP + is always arithmetic: numeric strings are added as numbers, and text that is not a number throws an error.

<?php
echo "5" + "5", "\n";  // numbers
echo "5" . "5", "\n";  // text

try {
    echo "Hello" + "World";
} catch (TypeError $e) {
    echo get_class($e) . ": " . $e->getMessage() . "\n";
}

If you see a number where you expected joined text, or Unsupported operand types: string + string, look for a + that should be a ..