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https://github.com/xzfc/cached-nix-shell
Instant startup time for nix-shell
https://github.com/xzfc/cached-nix-shell
nix nix-shell
Last synced: 5 days ago
JSON representation
Instant startup time for nix-shell
- Host: GitHub
- URL: https://github.com/xzfc/cached-nix-shell
- Owner: xzfc
- License: unlicense
- Created: 2019-09-18T14:23:00.000Z (over 5 years ago)
- Default Branch: master
- Last Pushed: 2024-11-24T23:00:19.000Z (3 months ago)
- Last Synced: 2025-02-09T06:05:44.220Z (12 days ago)
- Topics: nix, nix-shell
- Language: Rust
- Homepage: https://xzfc.github.io/cached-nix-shell/cached-nix-shell.1
- Size: 271 KB
- Stars: 217
- Watchers: 9
- Forks: 17
- Open Issues: 7
-
Metadata Files:
- Readme: readme.md
- License: LICENSE.MIT
Awesome Lists containing this project
- awesome-nix - cached-nix-shell - A `nix-shell` replacement that uses caching to open subsequent shells quickly. (Development / Discovery)
README
# cached-nix-shell
[](https://github.com/xzfc/cached-nix-shell/actions/workflows/test.yml?query=branch%3Amaster)
[](https://nixos.org/nixos/packages.html?attr=cached-nix-shell&channel=nixpkgs-unstable&query=cached-nix-shell)
[](https://xzfc.github.io/cached-nix-shell/cached-nix-shell.1)
`cached-nix-shell` is a caching layer for `nix-shell` featuring instant startup time on subsequent runs.
It supports NixOS and Linux.
## Installation
Install the release version from Nixpkgs:
```sh
nix-env -iA nixpkgs.cached-nix-shell
```
Or, install the latest development version from GitHub:
```sh
nix-env -if https://github.com/xzfc/cached-nix-shell/tarball/master
```
## Usage
Just replace `nix-shell` with `cached-nix-shell` in the shebang line:
```python
#! /usr/bin/env cached-nix-shell
#! nix-shell -i python3 -p python
print("Hello, World!")
```
Alternatively, call `cached-nix-shell` directly:
```sh
$ cached-nix-shell ./hello.py
$ cached-nix-shell -p python3 --run 'python --version'
```
Or use the `--wrap` option for programs that call `nix-shell` internally.
```sh
$ cached-nix-shell --wrap stack build
```
## Performance
```
$ time ./hello.py # first run; no cache used
cached-nix-shell: updating cache
Hello, World!
./hello.py 0.33s user 0.06s system 91% cpu 0.435 total
$ time ./hello.py
Hello, World!
./hello.py 0.02s user 0.01s system 97% cpu 0.029 total
```
## Caching and cache invalidation
`cached-nix-shell` stores environment variables set up by `nix-shell` and reuses them on subsequent runs.
It [traces](./nix-trace) which files are read by `nix` during an evaluation, and performs a proper cache invalidation if any of the used files are changed.
The cache is stored in `~/.cache/cached-nix-shell/`.
The following situations are covered:
* `builtins.readFile` is used
* `builtins.readDir` is used
* `import ./file.nix` is used
* updating `/etc/nix/nix.conf` or `~/.config/nix/nix.conf`
* updating nix channels
* updating `$NIX_PATH` environment variable
The following situations aren't handled by `cached-nix-shell` and may lead to staled cache:
* `builtins.fetchurl` or other network builtins are used (e.g. in [nixpkgs-mozilla])
[nixpkgs-mozilla]: https://github.com/mozilla/nixpkgs-mozilla
## Related
* https://discourse.nixos.org/t/speeding-up-nix-shell-shebang/4048
* There are related projects focused on using `nix-shell` for project developing:
* [direnv](https://direnv.net/) with [use_nix](https://github.com/direnv/direnv/wiki/Nix)
* [Cached and Persistent Nix shell with direnv integration](https://gist.github.com/mbbx6spp/731076cb8fc620b064b8e5b28fb1c796)
* [lorri](https://github.com/nix-community/lorri), a `nix-shell` replacement for project development
* [lorri #167](https://github.com/target/lorri/issues/167)
* [nix-develop](https://gitlab.com/mightybyte/nix-develop), universal build tool featuring cached `nd shell` command
* [https://github.com/rycee/home-manager/issues/447](https://github.com/rycee/home-manager/issues/447)