How do you work with strings in PHP?

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PHP has rich string support: different quote styles (with different interpolation behavior), concatenation, and a large library of string functions. Understanding the quote differences and the function set is everyday knowledge. ## Quotes: single vs double (interpolation) ```php name}"; // {} for complex expressions inside double quotes ``` The key difference: **double quotes interpolate variables** (`$name` is replaced with its value), **single quotes are literal** (faster, no interpolation). Use `{}` for complex expressions like object properties. ## Concatenation ```php $greeting = "Hello, " . $name . "!"; // . is the concatenation operator (NOT +) $greeting .= " Welcome."; // .= appends ``` PHP uses `.` for string concatenation (not `+`, which is numeric) — a common point of confusion. ## Heredoc and Nowdoc (multi-line) ```php $html = <<$name // heredoc — interpolates (like double quotes) HTML; $raw = <<<'TEXT' Literal $name // nowdoc (quoted label) — no interpolation (like single quotes) TEXT; ``` ## Essential string functions ```php strlen($s); // length strtoupper($s); strtolower($s); trim($s); // remove surrounding whitespace str_replace("old", "new", $s); strpos($s, "needle"); // find position (false if not found — use === false) substr($s, 0, 5); // extract a substring explode(",", $csv); // split into an array implode(",", $array); // join an array into a string sprintf("%.2f", 3.14159); // formatted output → "3.14" str_contains($s, "x"); // PHP 8: cleaner substring check ``` ## Multibyte safety (Unicode) ```php mb_strlen($s); // ✅ correct length for multi-byte (UTF-8) text strlen($s); // ⚠️ counts BYTES, not characters — wrong for non-ASCII ``` For non-ASCII/Unicode text, use the **`mb_*`** functions (`mb_strlen`, `mb_substr`) — the plain functions count bytes, not characters, breaking on multi-byte text. ## Why it matters String manipulation is pervasive in web development (building HTML, processing input, formatting output, parsing data), so understanding PHP's string handling is essential everyday knowledge. The most important practical points: the **single-vs-double-quote distinction** (double quotes interpolate variables, single quotes are literal) is fundamental and a frequent beginner confusion; PHP uses **`.` for concatenation** (not `+`); and PHP has a vast library of string functions for common tasks (search, replace, split/join, format). Critically, for any application handling non-English/Unicode text, knowing to use the **`mb_*` (multibyte) functions** instead of the plain ones (which count bytes, not characters, and corrupt multi-byte text) prevents real bugs. Fluency with PHP's quote behavior, concatenation, and string function library — including multibyte safety — is core knowledge for the constant string work that web development involves.