os.Stat and os.IsNotExist() can be used to check whether a particular file or directory exist or not.

File Exists

package main
import (
"log"
"os"
)
func main() {
fileinfo, err := os.Stat("temp.txt")
if os.IsNotExist(err) {
log.Fatal("File does not exist.")
}
log.Println(fileinfo)
}

Folder Exists

package main
import (
"log"
"os"
)
func main() {
folderInfo, err := os.Stat("temp")
if os.IsNotExist(err) {
log.Fatal("Folder does not exist.")
}
log.Println(folderInfo)
}