Add command to generate man pages

The climan package has a command that can be registered with any urfav
cli app to generate man pages.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

pkg/climan/cli.go

@@ -0,0 +1,75 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package climan
+
+import (
+	"fmt"
+	"io/ioutil"
+	"path/filepath"
+
+	"github.com/pkg/errors"
+	"github.com/urfave/cli"
+)
+
+var Command = cli.Command{
+	Name:   "gen-man",
+	Usage:  "generate man pages for the cli application",
+	Hidden: true,
+	Flags: []cli.Flag{
+		cli.StringFlag{
+			Name:  "format,f",
+			Usage: "specify the format in (md:man)",
+			Value: "md",
+		},
+		cli.IntFlag{
+			Name:  "section,s",
+			Usage: "section of the man pages",
+			Value: 1,
+		},
+	},
+	Action: func(clix *cli.Context) (err error) {
+		// clear out the usage as we use banners that do not display in man pages
+		clix.App.Usage = ""
+		dir := clix.Args().First()
+		if dir == "" {
+			return errors.New("directory argument is required")
+		}
+		var (
+			data string
+			ext  string
+		)
+		switch clix.String("format") {
+		case "man":
+			data, err = clix.App.ToMan()
+		default:
+			data, err = clix.App.ToMarkdown()
+			ext = "md"
+		}
+		if err != nil {
+			return err
+		}
+		return ioutil.WriteFile(filepath.Join(dir, formatFilename(clix, clix.Int("section"), ext)), []byte(data), 0644)
+	},
+}
+
+func formatFilename(clix *cli.Context, section int, ext string) string {
+	s := fmt.Sprintf("%s.%d", clix.App.Name, section)
+	if ext != "" {
+		s += "." + ext
+	}
+	return s
+}