brew/Library/Homebrew/cmd/help.rb

HOMEBREW_HELP = <<-EOS.freeze
Example usage:
  brew search [TEXT|/REGEX/]
  brew (info|home|options) [FORMULA...]
  brew install FORMULA...
  brew update
  brew upgrade [FORMULA...]
  brew uninstall FORMULA...
  brew list [FORMULA...]

Troubleshooting:
  brew config
  brew doctor
  brew install -vd FORMULA

Developers:
  brew create [URL [--no-fetch]]
  brew edit [FORMULA...]
  https://github.com/Homebrew/brew/blob/master/share/doc/homebrew/Formula-Cookbook.md

Further help:
  man brew
  brew help [COMMAND]
  brew home
EOS

# NOTE Keep the lenth of vanilla --help less than 25 lines!
# This is because the default Terminal height is 25 lines. Scrolling sucks
# and concision is important. If more help is needed we should start
# specialising help like the gem command does.
# NOTE Keep lines less than 80 characters! Wrapping is just not cricket.
# NOTE The reason the string is at the top is so 25 lines is easy to measure!

require "commands"

module Homebrew
  def help(cmd = nil, flags = {})
    # Resolve command aliases and find file containing the implementation.
    if cmd
      cmd = HOMEBREW_INTERNAL_COMMAND_ALIASES.fetch(cmd, cmd)
      path = Commands.path(cmd)
    end

    # Display command-specific (or generic) help in response to `UsageError`.
    if (error_message = flags[:usage_error])
      $stderr.puts path ? command_help(path) : HOMEBREW_HELP
      $stderr.puts
      onoe error_message
      exit 1
    end

    # Handle `brew` (no arguments).
    if flags[:empty_argv]
      $stderr.puts HOMEBREW_HELP
      exit 1
    end

    # Handle `brew (-h|--help|--usage|-?|help)` (no other arguments).
    if cmd.nil?
      puts HOMEBREW_HELP
      exit 0
    end

    # Resume execution in `brew.rb` for external/unknown commands.
    return if path.nil?

    # Display help for internal command (or generic help if undocumented).
    puts command_help(path)
    exit 0
  end

  private

  def command_help(path)
    help_lines = path.read.lines.grep(/^#:/)
    if help_lines.empty?
      opoo "No help text in: #{path}" if ARGV.homebrew_developer?
      HOMEBREW_HELP
    else
      help_lines.map do |line|
        line.slice(2..-1)
            .sub(/^  \* /, "#{Tty.highlight}brew#{Tty.reset} ")
            .gsub(/`(.*?)`/, "#{Tty.highlight}\\1#{Tty.reset}")
            .gsub(/<(.*?)>/, "#{Tty.em}\\1#{Tty.reset}")
            .gsub("@hide_from_man_page", "")
      end.join.strip
    end
  end
end