In a Newman command line, what does the `--folder` option select from a collection?

## What the option is for A saved Postman collection is one JSON document. Its `item` array holds the collection's contents, and an entry in that array is either a request or a folder carrying its own nested `item` list. A run with no selection walks the whole tree and sends every request in it. **`--folder` is the Newman command-line option that narrows a run to one part of that tree**, and it takes the **name or the id** of the thing you want to run. ## What the option becomes The CLI does not do the filtering itself. It converts the value into the run option the execution engine understands: **`entrypoint.execute`**, the single node a run starts from, together with a lookup strategy that says how the value is resolved. With one `--folder` value that strategy is the default **`idOrName`**, which resolves the value by finding an entry whose **id** or whose **name** equals it. The consequences worth memorising: - the value is compared against **ids and names**, so an id copied out of the file works exactly where a name does; - it is **equality against a single node**, not a path expression — you name one entry, never `Checkout/Payments`; - there is **no wildcard and no pattern**: a value either equals something or it matches nothing; - the **first match wins**, and the search takes **own children before deeper ones**, so a top-level entry beats a same-named entry buried further down; - a value that matches nothing is a **failure to start**, not a quiet empty run. ## Despite the name, it matches a request too The option is called `--folder`, and that name misleads in one specific way: **the lookup matches a request as well as a folder.** Requests and folders live side by side in the same `item` arrays and are resolved by the same id-or-name comparison, so a value naming a request resolves to that request and the run consists of exactly that one call. This is the quickest way to re-run a single request from a terminal, and it is also a trap, because a request that happens to share a folder's name can win the lookup. ## What actually executes Once the entry point resolves, the engine **flattens that subtree** into the ordered list of requests to send. Flattening means nested folders contribute their requests in place: a folder holding two requests and then a sub-folder of three yields five requests, the two first and the three after, because that is the order the entries occupy in the file's `item` arrays. Selection therefore changes **which** requests run and never the relative order of the ones that do. | Command line | Resolved entry point | What runs | |---|---|---| | no `--folder` | the collection itself | every request, in file order | | a value matching a folder | that folder | its subtree, flattened, in file order | | a value matching a request | that request | exactly one request | | a value matching nothing | none | nothing runs; the run fails to start | ## What it does not do - It does not **reorder** anything. Order is the position of entries in the file's `item` arrays, and selection preserves it inside the chosen subtree. - It does not **filter by pattern**. There is no substring or glob form, so "everything named like a smoke test" is not a selection this option can express. - It does not **change the sequence once a run is under way**. Jumping to a named request mid-run, or dropping the current one, is a different mechanism belonging to the sandbox's execution API rather than to selection. - It does not **detach the chosen entries from their place in the file**. Selection decides what executes; what an enclosing folder or the collection contributes to a request inside it is a separate subject. ## Why interviewers ask it Because the option looks obvious and is not. Candidates reliably assume three wrong things: that only a folder can match, that a nested folder needs a path, and that a misspelt value simply runs nothing. Being able to say **"it sets the run's entry point, resolved by id or name, first match wins, and that subtree is flattened in file order"** is the whole answer, and it explains every failure mode you will actually meet — the wrong folder ran because a name was duplicated, one request ran because a request shared a folder's name, or nothing ran at all because somebody renamed a folder in the shared collection.