Implement the `brew help` command

This is also used by `brew <cmd> --help`. The basic idea is to have the
documentation as a top level comment in each command file. To find these
comments, they have to be like this `#:`.

This is also used by the `brew man` command to keep the documentation
DRY, and for that there are now a header and footer for the man page.

1 files changed, 19 insertions, 0 deletions

diff --git a/Library/Homebrew/cmd/help.rb b/Library/Homebrew/cmd/help.rb
index f729c0e8c..76eef90a8 100644
--- a/Library/Homebrew/cmd/help.rb
+++ b/Library/Homebrew/cmd/help.rb
@@ -39,4 +39,23 @@ module Homebrew
   def help_s
     HOMEBREW_HELP
   end
+
+  def help_for_command(cmd)
+    cmd_path = if File.exist?(HOMEBREW_LIBRARY_PATH/"cmd/#{cmd}.sh")
+      HOMEBREW_LIBRARY_PATH/"cmd/#{cmd}.sh"
+    elsif ARGV.homebrew_developer? && File.exist?(HOMEBREW_LIBRARY_PATH/"dev-cmd/#{cmd}.sh")
+      HOMEBREW_LIBRARY_PATH/"dev-cmd/#{cmd}.sh"
+    elsif File.exist?(HOMEBREW_LIBRARY_PATH/"cmd/#{cmd}.rb")
+      HOMEBREW_LIBRARY_PATH/"cmd/#{cmd}.rb"
+    elsif ARGV.homebrew_developer? && File.exist?(HOMEBREW_LIBRARY_PATH/"dev-cmd/#{cmd}.rb")
+      HOMEBREW_LIBRARY_PATH/"dev-cmd/#{cmd}.rb"
+    end
+    return if cmd_path.nil?
+
+    cmd_path.read.
+      split("\n").
+      grep(/^#:/).
+      map { |line| line.slice(2..-1).delete("`").sub(/^  \* /, "brew ") }.
+      join("\n")
+  end
 end