Rubish: A Unix shell written in pure Ruby

Shell syntax is parsed and compiled to Ruby code, then executed by the Ruby VM. Fully Bash-compatible Rubish supports all the features of bash, and the shell syntax is fully compatible. You can run your existing bash scripts without modification. If you found any bash script that doesn't work in rubish, we consider it a bug, so please report it! Rubish is not just a shell implemented in Ruby, but a shell that deeply integrates Ruby. You can seamlessly mix shell commands and Ruby code, and even use Ruby's powerful features like blocks, iterators, and libraries in your shell scripts. Homebrew (macOS) brew tap amatsuda/rubish brew install --HEAD rubish From source git clone https://github.com/amatsuda/rubish.git cd rubish bundle install bundle exec exe/rubish bin/rubish is a small bash launcher that finds a usable Ruby on its own (probes ~/.rbenv/shims/ruby, /opt/homebrew/bin/ruby, /usr/local/bin/ruby, system Ruby; honors $RUBY). Use it when bundler isn't around — for example as a login shell, from a .app bundle, or anywhere PATH may be minimal: ./bin/rubish RUBY=/opt/homebrew/opt/ruby@3.4/bin/ruby ./bin/rubish # explicit override Usage Start an interactive shell: rubish script.sh Or you can even use this as a login shell! echo "$(which rubish)" | sudo tee -a /etc/shells chsh -s "$(which rubish)" Features beyond Bash Ruby conditions Use Ruby expressions as conditions in if, while, and until by wrapping them in { }. Shell variables are automatically bound as local variables in the Ruby expression: COUNT=5 if { count.to_i > 3 } echo 'count is greater than 3' end while { count.to_i > 0 } echo $COUNT COUNT=$((COUNT - 1)) done Ruby method call style Commands can be invoked using Ruby method call syntax with parentheses, in addition to the traditional UNIX style with spaces: # These are equivalent: ls -la ls('-la') # Arguments can be passed as method arguments: cat(file.txt) grep('pattern', file.txt) Method chaining Commands can be chained with Ruby methods using dot notation, forming a pipeline. The chain has to be opened by a parenthesized call, an array literal, or a block — once you're in chain context, subsequent methods can be bare: # Equivalent to `ls | sort` ls().sort # Equivalent to `ls | sort | uniq` ls().sort.uniq # Equivalent to `cat file.txt | grep error` cat(file.txt).grep(/error/) # Chains can be combined with blocks (see "Ruby iterator blocks" below) ls.select { it.end_with?('.rb') }.each { |f| puts f.upcase } The first segment needs the parens because bare cmd.method is ambiguous with paths and dotted filenames (./script.sh, file.tar.gz) — once () confirms a method-call form, the lexer knows it's safe to chain. Ruby iterator methods (.each, .map, .select, .detect) can take blocks to process command output line by line: ls.each { |f| puts f.upcase } cat(file.txt).map { |line| line.strip } ls.select { it.end_with?('.rb') } Inline Ruby evaluation Any line starting with a capital letter is evaluated as Ruby code directly. This means you can use Ruby classes, methods, and expressions right from the shell prompt without any special syntax: rubish$ Time.now => 2025-01-01 12:00:00 +0900 rubish$ Dir.glob('*.rb').sort => ["Gemfile", "Rakefile"] rubish$ ENV['HOME'] => "/Users/you" Ruby array and regexp literals Ruby array literals can be used directly in shell context. Rubish distinguishes them from glob patterns like [a-z] automatically: rubish$ [1, 2, 3].map { |x| x * x } => [1, 4, 9] Lambda expressions You can execute any Ruby code by surrounding it with a lambda expression (-> { }): rubish$ -> { 2 ** 10 } => 1024 Ruby-style function definitions In addition to the standard shell function syntax, rubish supports Ruby-style def...end with named parameters and splat args: def greet(name) echo "Hello, $name" end def log(level, *messages) echo "[$level] $messages" end greet world # => Hello, world Custom Ruby prompts Define your prompt as a Ruby function for full programmatic control. The function is called on every prompt render, so it can include dynamic content: def rubish_prompt branch = `git branch --show-current 2>/dev/null`.strip dir = Dir.pwd.sub(ENV['HOME'], '~') "\e[36m#{dir}\e[0m \e[33m#{branch}\e[0m $ " end def rubish_right_prompt Time.now.strftime('%H:%M:%S') end You can also use the traditional PS1/RPROMPT variables with bash (\X) or zsh (%X) escape codes. Slow shell initializations (e.g., rbenv init, nvm, pyenv) can be deferred to a background thread using lazy_load. The block runs immediately in the background, and its result (a string of shell code) is applied before the next prompt. This keeps shell startup instant: # In ~/.rubishrc lazy_load { `rbenv init - --no-rehash bash` } lazy_load { `nodenv init - bash` } Multiple lazy_load blocks run in parallel. By the time you type your first command, they're usually done. Running rubish -r disables all Ruby integration features (inline evaluation, lambdas, blocks, Ruby conditions, and array literals) for executing untrusted scripts

Rubish: A Unix shell written in pure Ruby

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