Build Your Own Shell - Rust

A POSIX-compliant shell in Rust, built for the CodeCrafters "Build Your Own Shell" challenge. Line editing and tab completion via rustyline; pipeline stages run concurrently, one thread per stage. A rewrite of my earlier C++ attempt.

What it supports

• Builtins: echo, pwd, cd (with ~ expansion), type, history, exit
• External commands resolved via PATH (checks the executable bit on every entry)
• Quoting: single quotes, double quotes, and backslash escaping, following the POSIX rule that inside double quotes \ only escapes ", \, $ and `
• Redirection: >, 1>, >>, 1>> for stdout, 2>, 2>> for stderr
• Pipelines: cmd1 | cmd2 | cmd3, one thread per stage
• Tab completion of builtins and all PATH executables
• History: history [n], history -r/-w/-a <file>, loads $HISTFILE on startup and saves on exit; appends only the entries added since the last save

$ ./your_program.sh
$ echo 'hello world' | tr a-z A-Z > /tmp/out.txt
$ history 2

What I learned

• How shell quoting works: the difference between single and double quotes, and when a backslash is special vs. literal
• How to wire up a command's input and output to pipes, files, or the terminal
• Running pipeline stages concurrently, so every command in a | b | c runs at the same time
• Adding line editing and tab completion with the rustyline library

Skeleton

File	Role
src/main.rs	The entire shell: REPL + history (main), quoting/redirection parsing (PipelineCommand::new), pipeline setup (Pipeline::new), builtins + external spawn (PipelineCommand::run), tab completion (CommandCompleter)