shell.nixIf you’ve opened this PDF, you already have your own motivation for -learning Nix. Here’s how it helps me. As a researcher, I tend to work on +
If you’ve opened this PDF, you already have your own motivation for +learning Nix. Here’s how it helps me. As a researcher, I tend to work on a series of short-term projects, mostly demos and prototypes. For each one, I typically develop some software using a compiler, often with some open source libraries. Often I use other tools to analyse data or @@ -310,21 +316,21 @@ generate documentation, for example.
would report errors when trying to build or run the project. Belatedly I would realise that my code relies on a library that they need to install. Or perhaps they had installed the library, but the version -they’re using is incompatible. +they’re using is incompatible.Using containers helped with the problem. However, I didn’t want to +
Using containers helped with the problem. However, I didn’t want to develop in a container. I did all my development in my nice, familiar, environment with my custom aliases and shell prompt. and then I containerised the software. This added step was annoying for me, and if my colleague wanted to do some additional development, they would probably extract all of the source code from the container first anyway. -Containers are great, but this isn’t the ideal use case for them.
+Containers are great, but this isn’t the ideal use case for them.Nix allows me to work in my custom environment, but forces me to specify any dependencies. It automatically tracks the version of each dependency -so that it can replicate the environment wherever and whenever it’s +so that it can replicate the environment wherever and whenever it’s needed.
Flakes are labeled as an experimental feature, so it might seem safer to avoid them. However, they have been in use for years, and there is -widespread adoption, so the aren’t going away any time soon. Flakes are +widespread adoption, so the aren’t going away any time soon. Flakes are easier to understand, and offer more features than the traditional Nix -approach. After weighing the pros and cons, I feel it’s better to learn +approach. After weighing the pros and cons, I feel it’s better to learn and use flakes; and this seems to be the general consensus.
There are hyphenated and unhyphenated versions of many Nix commands. +
There are hyphenated and un-hyphenated versions of many Nix commands.
For example, nix-shell and nix shell are two different commands.
Don’t confuse them!
Generally speaking, the unhyphenated versions are for working directly +
Generally speaking, the un-hyphenated versions are for working directly with flakes, while the hyphenated versions are for everything else.
In the case of Nix, the desired result is usually a derivation: -a software package that has been built and is ready for use. +a software package that has been built and make available for use. The Nix language has been designed for that purpose, and thus has some features you don’t typically find in general-purpose languages.
|
-
Although you probably won’t need to use it, there is another syntax for + Although you probably won’t need to use it, there is another syntax for flake references that you might encounter. This example
@@ -2226,7 +2316,7 @@ dependency defined in the previous example.
That depends on the programming languages your software is written in,
the build system you use, and more. There are Nix functions and tools
that can simplify much of this, and new, easier-to-use ones are released
-regularly. We’ll look at some of these in the next section.
+regularly. We’ll look at some of these in the next section.
@@ -2243,7 +2333,7 @@ detail.
Flakes are written in the Nix programming language, which is a functional language. As with most programming languages, there are many ways to achieve the same result. Below is an example you can follow when -writing your own flakes. I’ll explain the example in some detail. +writing your own flakes. I’ll explain the example in some detail.
@@ -2290,7 +2380,7 @@ dependencies in the input section should also be listed at the beginning
of the outputs section
❷.
-
Now it’s time to look at the content of the output section. If we want + Now it’s time to look at the content of the output section. If we want the package to be available for multiple systems (e.g., “x86_64-linux”, “aarch64-linux”, “x86_64-darwin”, and “aarch64-darwin”), we need to define the output for each of those @@ -2302,7 +2392,7 @@ outputs for each one. The The Below is a list of some functions that are commonly used in @@ -2337,7 +2427,7 @@ this section. The standard environment provides developPackage, callCabal2Nix<
-
This This
-
Now let’s look at the section I labeled Now let’s look at the section I labeled
@@ -2430,8 +2520,8 @@ see what it does.
This flake uses
@@ -2446,7 +2536,7 @@ unpacked.
The inputs section of the flake.
-
I’ve mentioned the Nix standard environment before, but I didn’t explain + I’ve mentioned the Nix standard environment before, but I didn’t explain
what it is. The standard environment, or 8.1. The Nix development shell
-
Let’s make a simple modification to the script. This will give you an + Let’s make a simple modification to the script. This will give you an opportunity to check your understanding of flakes.
@@ -2565,15 +2655,15 @@ opportunity to check your understanding of flakes.
The A development environment only allows you to develop the package. -Don’t expect the package outputs (e.g. executables) to be available -until you build them. However, our script doesn’t need to be compiled, -so can’t we just run it? +Don’t expect the package outputs (e.g. executables) to be available +until you build them. However, our script doesn’t need to be compiled, +so can’t we just run it?
@@ -2582,11 +2672,11 @@ bash: line 16: hello-flake: command not found
-
That worked before; why isn’t it working now? Earlier we used + That worked before; why isn’t it working now? Earlier we used
@@ -2607,7 +2697,7 @@ Hello from your flake!
-
Rather than typing the full path to the executable, it’s more convenient + Rather than typing the full path to the executable, it’s more convenient
to use
@@ -2617,7 +2707,7 @@ Hello from your flake!
-
Here’s a summary of the more common Nix commands. +Here’s a summary of the more common Nix commands.
-
Let’s enter a shell with the Glasgow Haskell Compiler ("ghc") and try to run the program. +Let’s enter a shell with the Glasgow Haskell Compiler ("ghc") and try to run the program.
@@ -3200,7 +3290,7 @@ executable hello-flake-haskell
At this point, I would normally write $ exit $ nix-shell -p "[ cabal-install (haskellPackages.ghcWithPackages (pkgs: with pkgs; [ hostname ]))]" $ cabal build -Warning: The package list for 'hackage.haskell.org' is 21 days old. +Warning: The package list for 'hackage.haskell.org' is 24 days old. Run 'cabal update' to get the latest list of available packages. Resolving dependencies... Build profile: -w ghc-9.4.8 -O1 @@ -3313,7 +3403,7 @@ different are the development shell and the package builder.+ For full logs, run 'nix log /nix/store/qhb3mvp8i87n58iwi3ldkwpin2m9zgya-source-hello-flake-haskell-sdist.tar.gz.drv'. +error: 1 dependencies of derivation '/nix/store/8qdbmfms1h0b60aqdxfk28fmdnlkcm1l-hello-flake-haskell-1.0.0.drv' failed to build
-
We’d like to share this package with others, but first we should do some + We’d like to share this package with others, but first we should do some
cleanup. When the package was built (automatically by the $ git add flake.lock
$ git commit -a -m 'initial commit'
-[master (root-commit) 39ade13] initial commit
+[master (root-commit) 666b827] initial commit
4 files changed, 137 insertions(+)
create mode 100644 Main.hs
create mode 100644 flake.lock
@@ -3378,20 +3468,20 @@ another directory and running it from there.
@@ -3426,7 +3516,7 @@ Initialized empty Git repository in /home/amy/codeberg/nix-book/source/new-flake
9.2.1. A simple Python program
-
Next, we’ll create a simple Python program. +Next, we’ll create a simple Python program. hello.py
@@ -3448,14 +3538,14 @@ Initialized empty Git repository in /home/amy/codeberg/nix-book/source/new-flake
-
Before we package the program, let’s verify that it runs. We’re going to
-need Python. By now you’ve probably figured out that we can write a
- Before we package the program, let’s verify that it runs. We’re going to
+need Python. By now you’ve probably figured out that we can write a
+
@@ -3478,7 +3568,7 @@ packages you need), and you want to experiment a bit first.
The command used here is |
Let’s enter a shell with Python so we can test the program.
+Let’s enter a shell with Python so we can test the program.
Next, create a Python script to build the package. We’ll use Python’s +
Next, create a Python script to build the package. We’ll use Python’s setuptools, but you can use other build tools. For more information on setuptools, see the Python @@ -3540,7 +3630,7 @@ args.
We won’t write flake.nix just yet. First we’ll try building the
+
We won’t write flake.nix just yet. First we’ll try building the
package manually.
The missing module error happens because we don’t have build available
+
The missing module error happens because we don’t have build available
in the temporary shell. We can fix that by adding “build” to the
temporary shell. When you need support for both a language and some of
-its packages, it’s best to use one of the Nix functions that are
+its packages, it’s best to use one of the Nix functions that are
specific to the programming language and build system. For Python, we
can use the withPackages function.
withPackages function.
Note that we’re now inside a temporary shell inside the previous +
Note that we’re now inside a temporary shell inside the previous
temporary shell! To get back to the original shell, we have to exit
twice. Alternatively, we could have done exit followed by the
nix-shell command.
Let’s start with the development shell. It seems logical to write +
Let’s start with the development shell. It seems logical to write something like the following.
Let’s try out the new flake.
+Let’s try out the new flake.
Why can’t it find flake.nix? Nix flakes only “see” files that are
+
Why can’t it find flake.nix? Nix flakes only “see” files that are
part of the repository. We need to add all of the important files to the
repo before building or running the flake.
We’d like to share this package with others, but first we should do some +
We’d like to share this package with others, but first we should do some
cleanup. When the package was built (automatically by the nix run
command), it created a flake.lock file. We need to add this to the
repo, and commit all important files.
$ git add flake.lock $ git commit -a -m 'initial commit' -[master (root-commit) 6bec7c3] initial commit +[master (root-commit) ddb5606] initial commit 4 files changed, 127 insertions(+) create mode 100644 flake.lock create mode 100644 flake.nix @@ -3818,7 +3905,7 @@ Python flake.10. Recipes
-@@ -3841,7 +3928,7 @@ are the recommended approach for development projects.This chapter provides examples of how to use Nix in a variety of scanarios. +
This chapter provides examples of how to use Nix in a variety of scenarios. Multiple types of recipes are provided are provided for some scenarios; comparing the different recipes will help you better understand Nix.
You can use
nix-shellto run scripts in arbitrary languages, providing the necessary dependencies. This is particularly convenient for -standalone scripts because you don’t need to create a repo and write a +standalone scripts because you don’t need to create a repo and write a separateflake.nix. The script should start with two "shebang" (#!) commands. The first should invokenix-shell. The second should declares the script @@ -3896,7 +3983,7 @@ mkShell {
Here’s a demonstration using the shell.
+Here’s a demonstration using the shell.
Here’s a demonstration using the shell.
+Here’s a demonstration using the shell.
Here’s a demonstration using the shell.
+Here’s a demonstration using the shell.
Ex: Access four Haskell packages
(pandoc-linear-table, pandoc-logic-proof, pandoc-columns and pandoc-maths-web)
@@ -4348,7 +4435,7 @@ mkShell {