Strings in PHP: Functions & Manipulation

Strings in PHP

A string is a sequence of characters, such as a name, a sentence, or an email address. PHP gives you flexible ways to create strings and a large set of built-in functions to search, change, and format text. Strings are everywhere in web work, from form data to database results.

Creating strings: single vs double quotes

Both single and double quotes create strings, but they behave differently.

<?php
$name = "Divya";

// Double quotes expand variables and escape sequences.
echo "Hello $name\n"; // Hello Divya (with a newline)

// Single quotes are literal - no variable expansion.
echo 'Hello $name';   // Hello $name
?>

Use double quotes when you want to insert variables; use single quotes for plain, literal text.

Concatenation

Join strings with the dot (.) operator.

<?php
$first = "Web";
$second = "Dev";

$combined = $first . " " . $second;
echo $combined; // Web Dev
?>

String interpolation

Inside double quotes, you can drop variables straight into the text. Use curly braces for clarity, especially with array values.

<?php
$user = ["name" => "Farhan"];

echo "Welcome, {$user['name']}!"; // Welcome, Farhan!
?>

Measuring and searching strings

<?php
$text = "Learn PHP";

echo strlen($text);          // 9  -> number of characters

// Find the position of a substring (0-based). Returns false if not found.
$pos = strpos($text, "PHP"); // 6

// Check if a string contains another (PHP 8).
var_dump(str_contains($text, "PHP")); // true
?>

Changing case and trimming

<?php
$name = "  priya kabra  ";

echo strtoupper($name);   // "  PRIYA KABRA  "
echo strtolower("HELLO"); // hello
echo ucwords("priya kabra"); // Priya Kabra (capitalise each word)

echo trim($name);         // "priya kabra" -> removes outer spaces
?>

Replacing and extracting

<?php
$sentence = "I like tea";

// Replace one substring with another.
echo str_replace("tea", "coffee", $sentence); // I like coffee

// Extract part of a string: substr(string, start, length).
echo substr("Jalgaon", 0, 3); // Jal
?>

Splitting and joining

<?php
$csv = "PHP,MySQL,HTML";

// Split a string into an array on a separator.
$parts = explode(",", $csv); // ["PHP", "MySQL", "HTML"]

// Join an array back into a string.
$joined = implode(" | ", $parts); // "PHP | MySQL | HTML"

echo $joined;
?>

Formatting numbers into strings

number_format() and sprintf() help present values neatly.

<?php
echo number_format(1234567.891, 2); // 1,234,567.89

// sprintf builds a formatted string without printing immediately.
$label = sprintf("Score: %d/%d", 8, 10);
echo $label; // Score: 8/10
?>

Common mistakes

• Expecting single quotes to expand variables. Only double quotes do.
• Treating strpos() returning 0 as "not found". Index 0 is a valid match; check with === false.
• Forgetting strings are zero-indexed when using substr().
• Confusing explode() and implode(). explode splits a string into an array; implode joins an array into a string.

FAQ

When do I use single vs double quotes? Use double quotes when you want variables inside the string. Use single quotes for literal text; they are marginally faster and avoid accidental expansion.

Why does strpos() sometimes give wrong results? If the match is at the very start, it returns 0, which looks falsy. Always compare with === false to test for "not found".

How do I check if a string contains another string? Use str_contains($haystack, $needle), added in PHP 8, which returns a clear boolean.

Keep learning

Back to the PHP & MySQL hub, revisit Functions in PHP, or continue to Object-Oriented Programming in PHP.

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