Change hub help to display man pages when available

Instead of displaying plain text help, `hub help <command>` will now
search for man pages to display.

* If `man` is available, hub first tries to locate the local
  `../man/hub-<command>.1` file relative to the `hub` executable. If
  found, open it with `man`. If not, execute `man 1 hub-<command>`.

* Otherwise, resort to displaying plain text help.

.gitignore

@@ -3,6 +3,7 @@
 /bin
 .bundle
 vendor/bundle/
+man/hub-*
 tmp/
 *.test
 target

commands/args.go

@@ -11,6 +11,7 @@ type Args struct {
 	Executable  string
 	GlobalFlags []string
 	Command     string
+	ProgramPath string
 	Params      []string
 	beforeChain []*cmd.Cmd
 	afterChain  []*cmd.Cmd

commands/help.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"sort"
 	"strings"
+	"path/filepath"
 
 	"github.com/github/hub/cmd"
 	"github.com/github/hub/git"
@@ -49,8 +50,43 @@ func runHelp(helpCmd *Command, args *Args) {
 	}
 
 	if c := lookupCmd(command); c != nil {
-		ui.Println(c.HelpText())
-		os.Exit(0)
+		manProgram, err := utils.CommandPath("man")
+		if err == nil {
+			man := cmd.New(manProgram)
+			manPage := "hub-" + c.Name()
+			manFile, err := localManPage(manPage, args)
+			if err == nil {
+				man.WithArg(manFile)
+			} else {
+				man.WithArgs("1", manPage)
+			}
+
+			err = man.Run()
+			if err == nil {
+				os.Exit(0)
+			} else {
+				os.Exit(1)
+			}
+		} else {
+			ui.Println(c.HelpText())
+			os.Exit(0)
+		}
+
+	}
+}
+
+func localManPage(cmd string, args *Args) (string, error) {
+	programPath, err := utils.CommandPath(args.ProgramPath)
+	if err != nil {
+		return "", err
+	}
+
+	manPath := filepath.Join(filepath.Dir(programPath), "..", "man", cmd + ".1")
+	_, err = os.Stat(manPath)
+	if err == nil {
+		return manPath, nil
+	} else {
+		return "", err
 	}
 }
 

commands/runner.go

@@ -67,6 +67,7 @@ func (r *Runner) Lookup(name string) *Command {
 
 func (r *Runner) Execute() ExecError {
 	args := NewArgs(os.Args[1:])
+	args.ProgramPath = os.Args[0]
 
 	if args.Command == "" {
 		printUsage()

utils/utils.go

@@ -56,6 +56,24 @@ func searchBrowserLauncher(goos string) (browser string) {
 	return browser
 }
 
+func CommandPath(cmd string) (string, error) {
+	if runtime.GOOS == "windows" {
+		cmd = cmd + ".exe"
+	}
+
+	path, err := exec.LookPath(cmd)
+	if err != nil {
+		return "", err
+	}
+
+	path, err = filepath.Abs(path)
+	if err != nil {
+		return "", err
+	}
+
+	return filepath.EvalSymlinks(path)
+}
+
 func DirName() (string, error) {
 	dir, err := os.Getwd()
 	if err != nil {