Workshop: Write Your Own Shell in Rust

One of the things developers use every day is a shell. It comes in many flavors, like bash, fish or zsh. Depending on your background, writing your own shell from scratch might either sound intimidating or pointless. We like to believe that it can be a fun way to gain more hands-on Rust experience. If you want to play with concepts like I/O, error handling, and syscalls, we invite you to participate in this workshop. Who knows, it could also be an opportunity to start your first mid-size Rust project!

Transcript

1. Write your own shell in Rust! Santiago Pastorino • Matthias Endler Rust Belt Rust Workshop 2018 Special Guest: Alex Crichton
2. About us Santiago Pastorino • WyeWorks co-founder • Ruby on Rails core team alumni • Started with Rust in 2017 • Member of Rust compiler NLL WG • Rust Latam conference organizer • Rust Montevideo Meetup organizer Matthias Endler • Started with Rust in 2015 • Member of the Rust Cologne Meetup • Runs Hello Rust YouTube channel
3. About the Workshop Goals • Learn some Rust • Intermediate concepts • Work on your first Rust project Structure • 6 hours total • split up into five blocks • roughly one hour per block
4. Schedule
5. Executing a Single Shell Command Block 2 Executing Multiple Commands Block 3 Implementing Shell-Builtins Block 4 Implementing Pipes Block 5 Bring Your Own Features ✨ Block 1 Setup Rust
6. Block 0 - Check your (nightly) Rust installation Main objective • Install nightly Rust using rustup or any other way. • Run `rustc -V` to see if you’re golden.
7. Block 1 - Executing a Single Shell Command Main objectives • Write a shell which can run a single command on a separate process. • Hint: Look for APIs in the standard library to do that. • Print the output to stdout. Bonus track • Write some unit tests to make sure that the shell works. • Make the code as idiomatic as possible.
8. Block 1 - Pseudo Code fn main() { loop { // Read line from standard input // “Parse” line into executable command // Execute the command in a separate process // Show output } }
9. Block 1 - Repository https://gitlab.com/mre_/rush mre_
10. Block 2 - Executing Multiple Commands Main objectives • Try to run two or more commands separated by ; in sequence. • Print all output in sequence to stdout. Bonus track • Implement && and || • Write an integration test. Share solutions here: http://tiny.cc/rustlang2 Repository: https://gitlab.com/mre_/rush
11. Block 2 - Executing Multiple Commands (Examples) > echo 1; echo 2 1 2 > true && echo "output" output > false && echo "output" > > true || echo "output" > false || echo "output" output > Main objectives Bonus track Share solutions here: http://tiny.cc/rustlang2 Repository: https://gitlab.com/mre_/rush tiny.cc/rust-slides
12. Block 3 - Implementing Shell-Builtins Main objectives • Implement the `cd` shell builtin. • Implement the `exit` shell builtin. Bonus track • Implement `exec` builtin
13. Block 3 - Implementing Shell-Builtins (Examples) > pwd /dir1 > cd /dir2 > pwd /dir2 > exit (Shell gets closed) > exec fish Welcome to fish, the friendly interactive shell Main objectives Bonus track Share solutions here: http://tiny.cc/rustlang2 Repository: https://gitlab.com/mre_/rush
14. Block 4 - Implementing Pipes Main objectives • Implement pipes, which are a way to feed the output of one command into another one. Syntax: command1|command2 Bonus track • Support multiple pipes: c1 | c2 | c3 • Add redirection: c1 > output.txt • Think about ways to make command representation more idiomatic.
15. Block 4 - Implementing Pipes (Examples) > echo foo | grep -c foo 1 Main objectives Bonus track > ps auxwww | grep fred | more > echo 1 > test.txt
16. Block 5 - Bring Your Own Features! Main objectives • It’s all free-style from here. What will you do next? ◦ Readline support ◦ Control signals ◦ Command completion ◦ use a grammar for parsing ◦ Implement more shell-builtins ◦ Surprise us! Bonus track • Get ✨ inspired ✨ by looking at existing shells, e.g. ◦ ion (Rust) ◦ elvish (Go) ◦ “the other rush” (Rust)