Getting count of files in directory using Go - go

Question

How might I get the count of items returned by io/ioutil.ReadDir()?
I have this code, which works, but I have to think isn't the RightWay(tm) in Go.
package main
import "io/ioutil"
import "fmt"
func main() {
files,_ := ioutil.ReadDir("/Users/dgolliher/Dropbox/INBOX")
var count int
for _, f := range files {
fmt.Println(f.Name())
count++
}
fmt.Println(count)
}
Lines 8-12 seem like way too much to go through to just count the results of ReadDir, but I can't find the correct syntax to get the count without iterating over the range. Help?

Answer 1

Found the answer in http://blog.golang.org/go-slices-usage-and-internals
package main
import "io/ioutil"
import "fmt"
func main() {
files,_ := ioutil.ReadDir("/Users/dgolliher/Dropbox/INBOX")
fmt.Println(len(files))
}

Answer 2

ReadDir returns a list of directory entries sorted by filename, so it is not just files. Here is a little function for those wanting to get a count of files only (and not dirs):
func fileCount(path string) (int, error){
i := 0
files, err := ioutil.ReadDir(path)
if err != nil {
return 0, err
}
for _, file := range files {
if !file.IsDir() {
i++
}
}
return i, nil
}

Answer 3

Starting with Go 1.16 (Feb 2021), a better option is os.ReadDir:
package main
import "os"
func main() {
d, e := os.ReadDir(".")
if e != nil {
panic(e)
}
println(len(d))
}
os.ReadDir returns fs.DirEntry instead of fs.FileInfo, which means that
Size and ModTime methods are omitted, making the process more efficient if
you just need an entry count.
https://golang.org/pkg/os#ReadDir

Answer 4

If you wanna get all files (not recursive) you can use len(files). If you need to just get the files without folders and hidden files just loop over them and increase a counter. And please don’t ignore errors

Answer 5

By looking at the code of ioutil.ReadDir
func ReadDir(dirname string) ([]fs.FileInfo, error) {
f, err := os.Open(dirname)
if err != nil {
return nil, err
}
list, err := f.Readdir(-1)
f.Close()
if err != nil {
return nil, err
}
sort.Slice(list, func(i, j int) bool { return list[i].Name() < list[j].Name() })
return list, nil
}
you would realize that it calls os.File.Readdir() then sorts the files.
In case of counting it, you don't need to sort, so you are better off calling os.File.Readdir() directly.
You can simply copy and paste this function then remove the sort.
But I did find out that f.Readdirnames(-1) is much faster than f.Readdir(-1).
Running time is almost half for /usr/bin/ with 2808 items (16ms vs 35ms).
So to summerize it in an example:
package main
import (
"fmt"
"os"
)
func main() {
f, err := os.Open(os.Args[1])
if err != nil {
panic(err)
}
list, err := f.Readdirnames(-1)
f.Close()
if err != nil {
panic(err)
}
fmt.Println(len(list))
}