# bellpull/which > Every export of bellpull/which, with its signature and doc comment: pathExtensions, extensionCandidates, searchPath, whichAllSync, whichSync, resolveExecutable and 5 more, plus 3 types. Source: https://bellpull.interlace.tools/docs/api/which ```ts import { pathExtensions, extensionCandidates, searchPath, … } from 'bellpull/which'; ``` ## Functions ### extensionCandidates The extensions tried for this command, in order. On Windows a command that already carries a dot may be complete as written, so the empty extension goes first — `which` does the same, and `whoami.cmd` on `PATH` depends on it. ```ts function extensionCandidates(command: string, options: WhichOptions): string[]; ``` | Parameter | Type | | :-- | :-- | | `command` | `string` | | `options` | `WhichOptions` | **Returns** `string[]` ### pathExtensions The `PATHEXT` list for this runtime, as an array. `['']` off Windows: no expansion. Exported because it is the one half of Windows resolution that can be *checked* from another platform: which extensions are tried, and in what order, is policy, whereas whether `C:\\tools\\npm.cmd` exists is a fact about a filesystem that is not here. ```ts function pathExtensions(options: WhichOptions): string[]; ``` | Parameter | Type | | :-- | :-- | | `options` | `WhichOptions` | **Returns** `string[]` ### resolveExecutable Where `command` resolves to for the purpose of **spawning it** — two `PATHEXT` attempts, not one, as `cross-spawn` does. `PATHEXT` answers "what would the shell run if I typed this", which is right for `which` and wrong for a spawner: an extensionless file with a `#!` line is still runnable here, because `spawn-args.ts` puts the interpreter in front of it. So the walk is repeated with expansion disabled. **One function, because two callers asking this differently is a bug and was one.** `spawn-args.ts` made both attempts and `run.ts` only the first, so on Windows a shebang script resolved for the parse and was then refused by `run()` with `NotFoundError`. Off Windows `pathExtensions` is always `['']` and the second attempt is the first, so the divergence was invisible to a 68 / 68 grading. ```ts function resolveExecutable(command: string, options: WhichOptions): Resolution | undefined; ``` | Parameter | Type | | :-- | :-- | | `command` | `string` | | `options` | `WhichOptions` | **Returns** `Resolution \| undefined` ### runPath `PATH` with every `node_modules/.bin` from `cwd` upward in front of it — `npm-run-path`'s contract (104 M/wk, 2 dependencies, last published 2024-08-26). Twelve lines rather than a sibling dependency (design R4): the walk stops at the filesystem root, which `resolve` of `'..'` reports by returning its own argument. ```ts function runPath(options: WhichOptions): string; ``` | Parameter | Type | | :-- | :-- | | `options` | `WhichOptions` | **Returns** `string` ### searchPath The directories this runtime would search, in order — the static projection of resolution (PRINCIPLES rule 6). A caller, or an agent, reads what *would* happen without running anything. It is also where the two refusals above become visible: an entry dropped for being empty or relative is listed with the reason, so a `PATH` that silently does less than its author expected says so. ```ts function searchPath(options: WhichOptions): SearchEntry[]; ``` | Parameter | Type | | :-- | :-- | | `options` | `WhichOptions` | **Returns** `SearchEntry[]` ### whichAllSync Every place `command` resolves to, best first. Empty when it resolves nowhere. `all` in `which`'s API; here it is the primitive and the single answer is the first of it, because "there are two `node`s on this `PATH`" is the finding an investigation wants and throwing away everything after the first is what stops it being available. ```ts function whichAllSync(command: string, options: WhichOptions): Resolution[]; ``` | Parameter | Type | | :-- | :-- | | `command` | `string` | | `options` | `WhichOptions` | **Returns** `Resolution[]` ### whichOrThrowSync Where `command` resolves to, throwing {@link NotFoundError} when it resolves nowhere. `which`'s own shape, for the callers that want it — and the one place in this package where not finding something is an exception, because the caller asked a question that has no other answer. ```ts function whichOrThrowSync(command: string, options: WhichOptions): Resolution; ``` | Parameter | Type | | :-- | :-- | | `command` | `string` | | `options` | `WhichOptions` | **Returns** `Resolution` ### whichSync Where `command` resolves to, or `undefined`. The non-throwing form, because "it is not installed" is an ordinary answer that a caller branches on — the same argument the `Result` in `run.ts` makes about a non-zero exit. ```ts function whichSync(command: string, options: WhichOptions): Resolution | undefined; ``` | Parameter | Type | | :-- | :-- | | `command` | `string` | | `options` | `WhichOptions` | **Returns** `Resolution \| undefined` ## Classes ### NotFoundError `Error` with the `code` a caller switches on, and the command it could not find. ```ts class NotFoundError extends Error { readonly command: string; readonly code = "ENOENT"; constructor(command: string); } ``` ## Constants ### delimiter The platform-specific file delimiter. ';' or ':'. ```ts const delimiter: ";" | ":"; ``` ### sep The platform-specific file separator. '\\' or '/'. ```ts const sep: "\\" | "/"; ``` ## Interfaces ### Resolution Where an executable was found, and what found it. ```ts interface Resolution { /** The absolute path of the file that would be executed. */ path: string; /** * The `PATH` entry it was found under, or `''` when the command carried its own path and * `PATH` was never consulted. This is the field no incumbent returns. */ from: string; /** * The extension appended from `PATHEXT` to find it — `.CMD`, `.EXE`. Always `''` off * Windows, where the file is executable or it is not. */ ext: string; } ``` ### SearchEntry One directory to search, and whether it was skipped and why. ```ts interface SearchEntry { /** The entry as it appeared on `PATH`, before quotes were stripped or it was resolved. */ raw: string; /** The absolute directory that will be searched, when it will be. */ dir?: string; /** Why it will not be, when it will not: a reader can see the hole rather than infer it. */ skipped?: 'empty' | 'relative'; } ``` ### WhichOptions ```ts interface WhichOptions { /** The ambient state. Required in spirit; defaulted only by the façades. */ runtime: Runtime; /** Override the `PATH` string. Overrides `runtime.env`'s, as `which`'s `path` does. */ path?: string | undefined; /** Override `PATHEXT`. `''` disables extension expansion entirely. */ pathExt?: string | undefined; /** Resolve relative entries and relative commands against this instead of `runtime.cwd`. */ cwd?: string | undefined; } ```