package main

import (
	"fmt"
	"os"
)

func main() {
	for _, s := range os.Args[1:] {
		fi, err := os.Stat(s)
		if err != nil {
			fmt.Fprintln(os.Stderr, err.Error())
		}
		mt := fi.ModTime()
		fmt.Printf("%d %s", mt, s)
	}
}

package main

import (
	"os"
	"fmt"
)

func main() {
	for _, s := range os.Args[1:] {
		fi, _ := os.Stat(s)
		mt := fi.ModTime()
		fmt.Printf("%d %s", mt, s)
	}
}

--- 
+++ 
@@ -1,13 +1,16 @@
 package main
 
 import (
+	"fmt"
 	"os"
-	"fmt"
 )
 
 func main() {
 	for _, s := range os.Args[1:] {
-		fi, _ := os.Stat(s)
+		fi, err := os.Stat(s)
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err.Error())
+		}
 		mt := fi.ModTime()
 		fmt.Printf("%d %s", mt, s)
 	}
mtime: Check for error return from Stat
