Path Segments & Regex Rules

## Capturing URI segments A **route parameter** captures part of the URL so the handler can use it. In Laravel you write it in curly braces inside the route's URI: ```php use Illuminate\Support\Facades\Route; Route::get('/news/{year}/{slug}', function (string $year, string $slug) { return "Article {$slug} from {$year}"; }); ``` A request to `/news/2026/budget-vote` runs the closure with `$year = '2026'` and `$slug = 'budget-vote'`. Key facts: - **Values are strings.** The router extracts text from the path; any conversion to a number, enum or model happens later. - **Names should be letters and underscores**, per the routing docs: `{news_id}`, not `{news-id}`. - **By default a parameter matches anything except `/`**, so each parameter covers exactly one path segment. - **Values are URL-decoded**, because the router matches against the decoded path. ## Optional segments Appending `?` makes a parameter optional: `/news/{year}/{month?}` matches both `/news/2026` and `/news/2026/05`. What happens when the segment is missing: 1. The router still matches the route, and the missing parameter is simply **absent** (not an empty string). 2. Laravel leaves absent parameters out of the list it passes to the handler. 3. If the handler's argument has a **default value**, that default is used. 4. If it has none, PHP receives too few arguments and throws an **`ArgumentCountError`**. That is why the docs insist on a default for every optional parameter: ```php Route::get('/news/{year}/{month?}', function (string $year, ?string $month = null) { // /news/2026 -> $month is null }); ``` Keep optional segments **at the end** of the URI. An optional segment followed by a required one cannot be left out in practice, and it makes URL generation confusing. ## How values reach the handler Laravel passes plain route parameters to the closure or controller method **by position**: the first captured segment goes to the first non-service argument, and so on. The argument names do not have to match the placeholders. Class-typed arguments such as `Illuminate\Http\Request` are resolved from the container and slotted in at their positions, and the docs recommend listing them **before** the route parameters. The exact splicing rules, and the bugs they produce when ignored, are a topic of their own. ## Two ways to default a missing segment | Where | How | Effect | |---|---|---| | Handler argument | `?string $month = null` or `string $page = '1'` | used when the segment is absent; the route knows nothing about it | | Route definition | `->defaults('month', '01')` | the route fills the parameter itself, so every consumer sees `'01'` | `->defaults()` is a method on the route instance. Laravel uses the same mechanism internally: `Route::redirect` and `Route::view` store their settings as route defaults. A route-level default is useful when middleware or `$request->route('month')` should see the value too, not just the handler. ## Reading a parameter outside the handler Any code with the request can read a parameter: `$request->route('year')` returns the value, and `$request->route('month', '01')` supplies a fallback. This is handy in middleware, where the handler's arguments are not available. ## A news-archive example ```php use App\Http\Controllers\ArchiveController; Route::get('/news/{year}/{month?}', [ArchiveController::class, 'index']) ->whereNumber(['year', 'month']); // ArchiveController public function index(string $year, ?string $month = null) { /* ... */ } ``` `/news/2026` lists the whole year; `/news/2026/05` lists May. ## Optional segments or a query string? Optional path segments are not the only way to express "maybe filter by month". The alternative is a query string, `/news/2026?month=05`, read with request input instead of a route parameter. - **Path segments** suit values that identify a resource or a canonical page: an archive for a year, or a year and a month. They are part of the route, show up in `route:list`, and can be constrained. - **Query strings** suit optional, combinable filters and sort orders: `?section=politics&sort=oldest`. They do not multiply route definitions, and their order does not matter. - A rule of thumb in interviews: if removing the value leaves a meaningful page and several such values combine freely, it belongs in the query string; if it names a distinct page, it belongs in the path. ## Pitfalls interviewers probe - **No default on an optional argument**: works for `/news/2026/05`, crashes with `ArgumentCountError` on `/news/2026`. - **Expecting an empty string** for a missing segment: the parameter is absent, so the default applies. - **Hyphens in parameter names**: stick to letters and underscores. - **Relying on argument names** to map values: plain values are positional, so keep argument order identical to the URI order.