commands: Add -O flag to server to open browser

Fixes gohugoio#13040

commands/server.go

@@ -40,6 +40,7 @@ import (
 	"time"
 
 	"github.com/bep/mclib"
+	"github.com/pkg/browser"
 
 	"github.com/bep/debounce"
 	"github.com/bep/simplecobra"
@@ -448,6 +449,7 @@ type serverCommand struct {
 	// Flags.
 	renderStaticToDisk  bool
 	navigateToChanged   bool
+	openBrowser         bool
 	serverAppend        bool
 	serverInterface     string
 	tlsCertFile         string
@@ -539,6 +541,7 @@ of a second, you will be able to save and see your changes nearly instantly.`
 	cmd.Flags().BoolVarP(&c.serverAppend, "appendPort", "", true, "append port to baseURL")
 	cmd.Flags().BoolVar(&c.disableLiveReload, "disableLiveReload", false, "watch without enabling live browser reload on rebuild")
 	cmd.Flags().BoolVarP(&c.navigateToChanged, "navigateToChanged", "N", false, "navigate to changed content file on live browser reload")
+	cmd.Flags().BoolVarP(&c.openBrowser, "openBrowser", "O", false, "open the site in a browser after server startup")
 	cmd.Flags().BoolVar(&c.renderStaticToDisk, "renderStaticToDisk", false, "serve static files from disk and dynamic files from memory")
 	cmd.Flags().BoolVar(&c.disableFastRender, "disableFastRender", false, "enables full re-renders on changes")
 	cmd.Flags().BoolVar(&c.disableBrowserError, "disableBrowserError", false, "do not show build errors in the browser")
@@ -998,6 +1001,13 @@ func (c *serverCommand) serve() error {
 
 	c.r.Println("Press Ctrl+C to stop")
 
+	if c.openBrowser {
+		// There may be more than one baseURL in multihost mode, open the first.
+		if err := browser.OpenURL(baseURLs[0].String()); err != nil {
+			c.r.logger.Warnf("Failed to open browser: %s", err)
+		}
+	}
+
 	err = func() error {
 		for {
 			select {