Build Your Own Shell — Go

A POSIX-flavored interactive shell built from scratch in Go as part of the CodeCrafters "Build Your Own Shell" challenge. Every feature — from raw terminal input to pipeline execution — is hand-rolled with no third-party shell libraries.

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Demo

$ echo "hello world"
hello world
$ ls | grep go
go.mod
go.sum
$ cat file.txt > out.txt 2> err.txt
$ sleep 5 &
[1] 12345
$ jobs
[1]+  Running    sleep 5 &
$ history 3
  8  ls | grep go
  9  cat file.txt > out.txt 2> err.txt
  10  sleep 5 &
$ exit

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Features

Core Shell

• REPL loop with $ prompt
• Raw-mode terminal — full keystroke control via golang.org/x/term
• Cursor-aware line editing (move, insert, delete at any position)
• Bell feedback on invalid operations

Input Parsing

• Single-quoted strings (no interpretation)
• Double-quoted strings with escape sequences
• Backslash escaping outside quotes
• Shell variable expansion: $VAR and ${VAR}
• && sequential AND chaining
• & background execution

I/O

• | multi-stage pipelines
• > / >> stdout redirection (overwrite / append)
• 2> / 2>> stderr redirection (overwrite / append)

Built-in Commands

• echo [-n] [-e] [-E] — with escape sequence interpretation
• cd [path|~] — with home directory support
• pwd
• type — identifies builtins vs external executables with full path
• history [-r/-w/-a] [file] — session history with file persistence
• jobs — lists background jobs with +/- markers and Running/Done status
• complete -C <program> <command> — programmable completion
• declare VAR=val / -p VAR — shell variables
• exit — flushes history to $HISTFILE

Tab Completion

• Complete commands (builtins + PATH executables)
• Complete file/directory paths (appends / for dirs)
• Longest-common-prefix completion on multiple matches
• Double-Tab to list all candidates
• Programmable completion via -C external programs (COMP_LINE / COMP_POINT)

History

• Up/Down arrow navigation
• Load from $HISTFILE on startup, save on exit
• history -r/-w/-a for manual file management

Background Jobs

• cmd & runs command asynchronously
• Goroutine-based reaping via a doneCh channel
• jobs with most-recent (+) and second-most-recent (-) markers

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Project Structure

app/
├── main.go          # REPL loop, built-in dispatch
├── ReadLine.go      # Raw terminal I/O, cursor control, tab completion
├── ParseInput.go    # Single-pass tokenizer: quotes, escapes, operators, variables
├── PipeLine.go      # Multi-stage pipe execution
├── ExternalComm.go  # External command runner + I/O redirection
├── jobs.go          # Background job control
├── History.go       # History navigation and file persistence
├── comlete.go       # Programmable completion (-C) support
├── cd.go            # cd builtin
├── echo.go          # echo builtin with -n/-e/-E flags
├── variables.go     # Shell variable store (declare)
└── yahya_library.go # Generic MergeSort, Binary Search, Pair[T,U]

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Running Locally

Requirements: Go 1.25+

./your_program.sh

Submit to CodeCrafters:

git push origin master