2023-06-30 09:00:03 +00:00
# Debug with `nix repl`
2023-06-23 14:22:13 +00:00
2023-06-24 04:24:00 +00:00
We've used `nix repl '<nixpkgs>'` many times to check the source code in this guide, it's a powerful tool to help us understand how things work in Nix.
2023-06-23 14:22:13 +00:00
Better take a look at the help message of `nix repl` :
```
› < nixpkgs > '
Welcome to Nix 2.13.3. Type :? for help.
Loading installable ''...
Added 17755 variables.
nix-repl> :?
The following commands are available:
< expr > Evaluate and print expression
< x > = < expr > Bind expression to variable
:a < expr > Add attributes from resulting set to scope
:b < expr > Build a derivation
:bl < expr > Build a derivation, creating GC roots in the working directory
:e < expr > Open package or function in $EDITOR
:i < expr > Build derivation, then install result into current profile
:l < path > Load Nix expression and add it to scope
:lf < ref > Load Nix flake and add it to scope
:p < expr > Evaluate and print expression recursively
:q Exit nix-repl
:r Reload all files
:sh < expr > Build dependencies of derivation, then start nix-shell
:t < expr > Describe result of evaluation
:u < expr > Build derivation, then start nix-shell
:doc < expr > Show documentation of a builtin function
:log < expr > Show logs for a derivation
:te [bool] Enable, disable or toggle showing traces for errors
```
Some expressions that I use frequently: `:lf <ref>` , `:e <expr>` .
`:e <expr>` is very intuitive, so I won't repeat it. let's take a look at `:lf <ref>` :
```nix
# cd into my nix-config repo(you should replace it with your own nix-config repo)
›
# enter nix repl
›
Welcome to Nix 2.13.3. Type :? for help.
# load my nix flake and add it to scope
nix-repl> :lf .
Added 16 variables.
# press <TAB> to see what we have in scope
nix-repl>< TAB >
# ......omit some outputs
__isInt nixosConfigurations
__isList null
__isPath outPath
__isString outputs
__langVersion packages
# ......omit some outputs
# check what's in inputs
nix-repl> inputs.< TAB >
inputs.agenix inputs.nixpkgs
inputs.darwin inputs.nixpkgs-darwin
inputs.home-manager inputs.nixpkgs-unstable
inputs.hyprland inputs.nixpkgs-wayland
inputs.nil
inputs.nixos-generators
# check what's in inputs.nil
nix-repl> inputs.nil.packages.
inputs.nil.packages.aarch64-darwin
inputs.nil.packages.aarch64-linux
inputs.nil.packages.x86_64-darwin
inputs.nil.packages.x86_64-linux
# check the outputs of my nix flake
nix-repl> outputs.nixosConfigurations.< TAB >
outputs.nixosConfigurations.ai
outputs.nixosConfigurations.aquamarine
outputs.nixosConfigurations.kana
outputs.nixosConfigurations.ruby
nix-repl> outputs.nixosConfigurations.ai.< TAB >
outputs.nixosConfigurations.ai._module
outputs.nixosConfigurations.ai._type
outputs.nixosConfigurations.ai.class
outputs.nixosConfigurations.ai.config
outputs.nixosConfigurations.ai.extendModules
outputs.nixosConfigurations.ai.extraArgs
outputs.nixosConfigurations.ai.options
outputs.nixosConfigurations.ai.pkgs
outputs.nixosConfigurations.ai.type
nix-repl> outputs.nixosConfigurations.ai.config.
outputs.nixosConfigurations.ai.config.age
outputs.nixosConfigurations.ai.config.appstream
outputs.nixosConfigurations.ai.config.assertions
outputs.nixosConfigurations.ai.config.boot
outputs.nixosConfigurations.ai.config.console
outputs.nixosConfigurations.ai.config.containers
# ......omit other outputs
nix-repl> outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.< TAB >
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.activation
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.activationPackage
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.emptyActivationPath
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.enableDebugInfo
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.enableNixpkgsReleaseCheck
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.extraActivationPath
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.extraBuilderCommands
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.extraOutputsToInstall
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.extraProfileCommands
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.file
# ......omit other outputs
nix-repl> outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.sessionVariables.< TAB >
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.sessionVariables.BROWSER
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.sessionVariables.DELTA_PAGER
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.sessionVariables.EDITOR
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.sessionVariables.TERM
# ......omit other outputs
# check the value of `TERM`
nix-repl> outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.sessionVariables.TERM
"xterm-256color"
# check all files defined by `home.file`
nix-repl> outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.file.< TAB >
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.file..bash_profile
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.file..bashrc
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.file..config/fcitx5/profile
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.file..config/fcitx5/profile-bak
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.file..config/i3/config
outputs.nixosConfigurations.ai.config.home-manager.users.ryan.home.file..config/i3/i3blocks.conf
#......
```
2023-06-24 04:24:00 +00:00
As we can see, we can check every attribute of my flake in the REPL after loading it, which is very convenient for debugging.
