add an on-select command (#864)

app.go

@@ -413,7 +413,7 @@ func (app *app) loop() {
 			curr, err := app.nav.currFile()
 			if err == nil {
 				if d.path == app.nav.currDir().path {
-					app.ui.loadFile(app.nav, true)
+					app.ui.loadFile(app, true)
 				}
 				if d.path == curr.path {
 					app.ui.dirPrev = d
@@ -462,7 +462,7 @@ func (app *app) loop() {
 			app.ui.draw(app.nav)
 		case <-app.ticker.C:
 			app.nav.renew()
-			app.ui.loadFile(app.nav, false)
+			app.ui.loadFile(app, false)
 			app.ui.draw(app.nav)
 		}
 	}
@@ -536,7 +536,7 @@ func (app *app) runShell(s string, args []string, prefix string) {
 		anyKey()
 	}
 
-	app.ui.loadFile(app.nav, true)
+	app.ui.loadFile(app, true)
 
 	switch prefix {
 	case "%":

doc.go

@@ -187,6 +187,7 @@ The following special shell commands are used to customize the behavior of lf wh
     delete
     pre-cd
     on-cd
+    on-select
     on-quit
 
 The following commands/keybindings are provided by default:
@@ -904,6 +905,10 @@ This shell command can be defined to be executed before changing a directory.
 
 This shell command can be defined to be executed after changing a directory.
 
+    on-select
+
+This shell command can be defined to be executed after the selection changes.
+
     on-quit
 
 This shell command can be defined to be executed before quit.