nix-shell workshop

cpp program with custom library

the example features a self made library called mylib which is packaged using nix - see mylib.nix and default.nix how that is done.

the library mylib is used in a program called main.

how to build: enter environment by typing nix-shell in ./c-programs afterwards change directory cd main and run make

finally run ./main to see the ultimate answer:

./main 
hello world from the #cccamp2015, the answer is 
42

go programs

this example features a minimal webserver. It shows a "Hello World" html page on port 8080. To start the Server run:

cd goexample
nix-shell    
go run helloworld.go

qt program

this example features a qt5 console application console:

run cd qt-program and nix-shell to get a qt5 including environment. afterwards run qmake and make to generate the console binary. finally run ./console to obtain:

hello beautiful world, from #cccamp2015! 

perl

run cd perl and inside there run nix-shell -p perlPackages.WWWCurl -p perl, afterwards run ./www_curl_easy.pl and see strange gibberish strings coming to stdout - ooooohhh what is that?

note: no danger for your system, just carry on, there is much to see!

python

enter environment by typing nix-shell in ./python-program

run simpleCurl by running python simpleCurl http://test.de

it will output the html of http://test.de

rust

enter the environment by typing nix-shell in ./rust-programs.

afterwards run hello-rust and see the output:

Hello, world!

questions

• pick 3 of the examples above and build the software as described using nix-shell and run the programs to see that they work
• is nix-shell limited to run exclusivly on NixOS or can it be used on other platforms as well?
• why does the cpp program with custom library find the mylib.so, as for instance, pkg-config is not used at all?
• use nix-shell -p clang (instead of using nix-shell with default.nix) and compile the cpp program+library example using llvm's clang++ instead of g++
• you probably noticed that when you use nix-shell -p clang that it ignores default.nix and does not build mylib and thus you have to modify the Makefiles of the library and main program to get it working but there is a different approach. that is: use a different standard environment or stdenv for short. see default-clang.nix where clangStdenv is used instead of stdenv
• when you compile the cpp program with custom library, can you still run the program from a different environment where you don't use nix-shell prior execution? also try this for the python example above and compare the results!
• write a default.nix for the perl example, so that you don't need to pass -p on the shell anymore
• what is the effect of running nix-shell --pure in one shell vs. running nix-shell in a second shell? use the export command in either to see what parameters changed. use https://www.diffchecker.com/diff to compare the values you obtained
• issue nix-env -qaP | grep python and see that there is python 2.x and 3.x; you can filter the search further using | grep -v foo to filter out all lines containing 'foo'. figure out how to get a nix-shell with python 2.x and one with python 3.x, issue python --version to verify that you got the right version!
• nix-shell can be used with a local checkout of nixpkgs, nix-shell -I nixpkgs=/foo/bar/nixpkgs --pure -p cmake, therefore clone nixpkgs 'master' from https://github.com/nixos/nixpkgs and issue the above command. compare the result to nix-shell -I nixpkgs=/foo/bar/nixpkgs --pure -p cmake in regards to amount of downloads/ build targets and compare the two outcomes
• what is the major difference between using nix-shell and myEnvFun, read https://lastlog.de/blog/posts/developing_software_using_nixos.html to learn about myEnvFun. afterwards adapt the cpp program with custom library to use myEnvFun instead of nix-shell
• play with persistent nix-shell environments, see https://nixos.org/wiki/Development_Environments#Making_a_Persistent_nix-shell_Environment

documentation

• https://nixos.org/wiki/Development_Environments
• https://lastlog.de/blog/posts/developing_software_using_nixos.html

license

please feel free to copy as this repo is public domain