etash

ExTremely Ahh SHell — a shell written from the ground up in Rust with a custom lexer, parser, and executor.

Building

cargo build --release
./target/release/etash

Features

Interactive editing

• History — up/down arrows, Ctrl+R reverse search, persisted to ~/.etash_history
• Tab completion — first word completes commands from $PATH and builtins; subsequent words complete filenames
• Line editing — Ctrl+A/E (start/end), Ctrl+W (delete word), Ctrl+D (exit)

Commands

ls | grep foo | wc -l        # pipelines
cmd1; cmd2                   # sequential
cmd1 && cmd2                 # and
cmd1 || cmd2                 # or
sleep 10 &                   # background
(cd /tmp && ls)              # subshell
ls *.rs                      # glob expansion

Redirects

Syntax	Effect
cmd > file	redirect stdout
cmd >> file	append stdout
cmd < file	redirect stdin
cmd 2> file	redirect stderr
cmd 2>&1	stderr to stdout
cmd > file 2>&1	both to file

Variables and expansion

NAME=etash
export PATH="/usr/local/bin:$PATH"
echo "Hello, $NAME"        # variable expansion
echo "pid: $$"             # shell pid
echo "status: $?"          # last exit code
echo "${NAME}_rc"          # braced expansion
cd ~/projects              # tilde expansion
unset NAME

Builtins

Command	Description
cd [dir]	change directory (no arg → $HOME)
pwd	print working directory
export KEY=val	set and export variable
unset KEY	remove variable
fg [%N]	bring job N to foreground
bg [%N]	resume job N in background
exit [code]	exit with optional status

Job control

• Ctrl+Z stops the foreground process and parks it in the job table
• fg / bg resume stopped jobs
• Completed background jobs are reported at the next prompt: [1] done pid=X exit=0

Startup file

etash reads ~/.etashrc on startup:

export EDITOR=vim
HISTSIZE=1000
# comments and blank lines are ignored

Architecture

src/
  lexer/      tokenizer — words, quotes, escapes, redirects, operators
  parser/     shunting-yard parser → AST
  shell/      state — variables, exports, cwd, word expansion
  executor/   runs AST nodes, pipelines, redirects, job control, builtins
  main.rs     REPL (rustyline)
tests/
  lexer.rs    }
  parser.rs   }  69 tests
  shell.rs    }

Not yet implemented

• Pipelines with non-command stages ((a; b) | cmd)
• Command substitution ($(cmd))
• Arithmetic expansion ($((expr)))
• Here-documents (<<EOF)
• Shell functions
• source / .
• ~username expansion
• jobs builtin