Strings and String Functions

PHP includes an extensive library of built-in string functions for searching, formatting, and transforming text, alongside two different quoting styles with different behaviour.

Single vs Double Quotes

Double-quoted strings support variable interpolation and escape sequences like \n; single-quoted strings treat almost everything literally, which is slightly faster when interpolation isn't needed.

$name = "Bongani";
echo "Hello, $name!\n";      // Hello, Bongani!
echo 'Hello, $name!\n';      // Hello, $name!\n (literal text)

Common String Functions

A handful of built-in functions cover the majority of everyday string manipulation needs.

• strlen($str) — number of characters.
• strtolower() / strtoupper() — case conversion.
• str_replace($search, $replace, $str) — find and replace text.
• substr($str, $start, $length) — extract a portion of a string.
• trim($str) — remove whitespace from both ends.

Common Mistakes

• Using single quotes when variable interpolation was actually intended, resulting in the literal variable name being printed.
• Forgetting that string indices in PHP start at 0 when using functions like substr.
• Not trimming user input before validating it, so accidental leading/trailing spaces cause valid input to be rejected.
• Mixing up the argument order in str_replace, which is (search, replace, subject) — the reverse of what some other languages use.