docs: document lookupFileArg syntax in nix-build

Change-Id: Ib6d68594a16132805ba5d97526e16f7b3633117e
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Qyriad 2024-05-20 22:21:14 -06:00
parent 1818752c5c
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@ -29,10 +29,40 @@ created (`result`, `result-2`, and so on).
If no *paths* are specified, then `nix-build` will use `default.nix` in If no *paths* are specified, then `nix-build` will use `default.nix` in
the current directory, if it exists. the current directory, if it exists.
If an element of *paths* starts with `http://` or `https://`, it is ## Path Syntax
interpreted as the URL of a tarball that will be downloaded and unpacked
to a temporary location. The tarball must include a single top-level A given element of *paths* may take one of a few different forms, the first being a simple filesystem path, e.g. `nix-build /tmp/some-file.nix`.
directory containing at least a file named `default.nix`. It may also be a [search path](./env-common.html#env-NIX_PATH) like `<nixpkgs>`, which is convenient to use with `--attr`/`-A`:
```console
$ nix-build '<nixpkgs>' -A firefox
```
(Note the quotation marks around `<nixpkgs>`, which will be necessary in most Unix shells.)
If an element of *paths* starts with `http://` or `https://`, it is interpreted as the URL of a tarball which will be fetched and unpacked.
Lix will then `import` the unpacked directory, so these tarballs must include at least single top-level directory with a file called `default.nix`
For example, you could build from a specific version of Nixpkgs with something like:
```console
$ nix-build "https://github.com/NixOS/nixpkgs/archive/refs/heads/release-23.11.tar.gz" -A firefox
```
If a path starts with `flake:`, the rest of the argument is interpreted as a [flakeref](./new-cli/nix3-flake.html#flake-references) (see `nix flake --help` or `man nix3-flake`), which requires the "flakes" experimental feature to be enabled.
Lix will fetch the flake, and then `import` its unpacked directory, so the flake must include a file called `default.nix`.
For example, the flake analogue to the above `nix-build` commands are:
```console
$ nix-build flake:nixpkgs -A firefox
$ nix-build flake:github:NixOS/nixpkgs/release-23.11 -A firefox
```
Finally, for legacy reasons, if a path starts with `channel:`, the rest of the argument is interpreted as the name of a channel to fetch from `https://nixos.org/channels/$CHANNEL_NAME/nixexprs.tar.xz`.
> **NOTE:**: any of the special syntaxes may always be disambiguated by prefixing the path.
> For example: a file in the current directory called `<nixpkgs>'` can be addressed as `./<nixpkgs>`, to escape the special interpretation.
## Notes
`nix-build` is essentially a wrapper around `nix-build` is essentially a wrapper around
[`nix-instantiate`](nix-instantiate.md) (to translate a high-level Nix [`nix-instantiate`](nix-instantiate.md) (to translate a high-level Nix