List directory in Go

Question

I\'ve been trying to figure out how to simply list the files and folders in a single directory in Go.

I\'ve found filepath.Walk, but it goes into sub-directories aut

Answer 1

Go 1.16 (Q1 2021) will propose, with CL 243908 and CL 243914 , the ReadDir function, based on the FS interface:

// An FS provides access to a hierarchical file system.
//
// The FS interface is the minimum implementation required of the file system.
// A file system may implement additional interfaces,
// such as fsutil.ReadFileFS, to provide additional or optimized functionality.
// See io/fsutil for details.
type FS interface {
    // Open opens the named file.
    //
    // When Open returns an error, it should be of type *PathError
    // with the Op field set to "open", the Path field set to name,
    // and the Err field describing the problem.
    //
    // Open should reject attempts to open names that do not satisfy
    // ValidPath(name), returning a *PathError with Err set to
    // ErrInvalid or ErrNotExist.
    Open(name string) (File, error)
}

That allows for "os: add ReadDir method for lightweight directory reading":
See commit a4ede9f:

// ReadDir reads the contents of the directory associated with the file f
// and returns a slice of DirEntry values in directory order.
// Subsequent calls on the same file will yield later DirEntry records in the directory.
//
// If n > 0, ReadDir returns at most n DirEntry records.
// In this case, if ReadDir returns an empty slice, it will return an error explaining why.
// At the end of a directory, the error is io.EOF.
//
// If n <= 0, ReadDir returns all the DirEntry records remaining in the directory.
// When it succeeds, it returns a nil error (not io.EOF).
func (f *File) ReadDir(n int) ([]DirEntry, error) 

// A DirEntry is an entry read from a directory (using the ReadDir method).
type DirEntry interface {
    // Name returns the name of the file (or subdirectory) described by the entry.
    // This name is only the final element of the path, not the entire path.
    // For example, Name would return "hello.go" not "/home/gopher/hello.go".
    Name() string
    
    // IsDir reports whether the entry describes a subdirectory.
    IsDir() bool
    
    // Type returns the type bits for the entry.
    // The type bits are a subset of the usual FileMode bits, those returned by the FileMode.Type method.
    Type() os.FileMode
    
    // Info returns the FileInfo for the file or subdirectory described by the entry.
    // The returned FileInfo may be from the time of the original directory read
    // or from the time of the call to Info. If the file has been removed or renamed
    // since the directory read, Info may return an error satisfying errors.Is(err, ErrNotExist).
    // If the entry denotes a symbolic link, Info reports the information about the link itself,
    // not the link's target.
    Info() (FileInfo, error)
}

src/os/os_test.go#testReadDir() illustrates its usage:

    file, err := Open(dir)
    if err != nil {
        t.Fatalf("open %q failed: %v", dir, err)
    }
    defer file.Close()
    s, err2 := file.ReadDir(-1)
    if err2 != nil {
        t.Fatalf("ReadDir %q failed: %v", dir, err2)
    }

Answer 2

ioutil.ReadDir is a good find, but if you click and look at the source you see that it calls the method Readdir of os.File. If you are okay with the directory order and don't need the list sorted, then this Readdir method is all you need.

Answer 3

We can get a list of files inside a folder on the file system using various golang standard library functions.

1. filepath.Walk
2. ioutil.ReadDir
3. os.File.Readdir

package main

import (
    "fmt"
    "io/ioutil"
    "log"
    "os"
    "path/filepath"
)

func main() {
    var (
        root  string
        files []string
        err   error
    )

    root := "/home/manigandan/golang/samples"
    // filepath.Walk
    files, err = FilePathWalkDir(root)
    if err != nil {
        panic(err)
    }
    // ioutil.ReadDir
    files, err = IOReadDir(root)
    if err != nil {
        panic(err)
    }
    //os.File.Readdir
    files, err = OSReadDir(root)
    if err != nil {
        panic(err)
    }

    for _, file := range files {
        fmt.Println(file)
    }
}

1. Using filepath.Walk

The path/filepath package provides a handy way to scan all the files in a directory, it will automatically scan each sub-directories in the directory.

func FilePathWalkDir(root string) ([]string, error) {
    var files []string
    err := filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
        if !info.IsDir() {
            files = append(files, path)
        }
        return nil
    })
    return files, err
}

2. Using ioutil.ReadDir

ioutil.ReadDir reads the directory named by dirname and returns a list of directory entries sorted by filename.

func IOReadDir(root string) ([]string, error) {
    var files []string
    fileInfo, err := ioutil.ReadDir(root)
    if err != nil {
        return files, err
    }

    for _, file := range fileInfo {
        files = append(files, file.Name())
    }
    return files, nil
}

3. Using os.File.Readdir

Readdir reads the contents of the directory associated with file and returns a slice of up to n FileInfo values, as would be returned by Lstat, in directory order. Subsequent calls on the same file will yield further FileInfos.

func OSReadDir(root string) ([]string, error) {
    var files []string
    f, err := os.Open(root)
    if err != nil {
        return files, err
    }
    fileInfo, err := f.Readdir(-1)
    f.Close()
    if err != nil {
        return files, err
    }

    for _, file := range fileInfo {
        files = append(files, file.Name())
    }
    return files, nil
}

Benchmark results.

Get more details on this Blog Post

Answer 4

From your description, what you probably want is os.Readdirnames.

func (f *File) Readdirnames(n int) (names []string, err error)

Readdirnames reads the contents of the directory associated with file and returns a slice of up to n names of files in the directory, in directory order. Subsequent calls on the same file will yield further names.

...

If n <= 0, Readdirnames returns all the names from the directory in a single slice.

Snippet:

file, err := os.Open(path)
if err != nil {
    return err
}
defer file.Close()
names, err := file.Readdirnames(0)
if err != nil {
    return err
}
fmt.Println(names)

Credit to SquattingSlavInTracksuit's comment; I'd have suggested promoting their comment to an answer if I could.

Answer 5

You can try using the ReadDir function in the io/ioutil package. Per the docs:

ReadDir reads the directory named by dirname and returns a list of sorted directory entries.

The resulting slice contains os.FileInfo types, which provide the methods listed here. Here is a basic example that lists the name of everything in the current directory (folders are included but not specially marked - you can check if an item is a folder by using the IsDir() method):

package main

import (
    "fmt"
    "io/ioutil"
     "log"
)

func main() {
    files, err := ioutil.ReadDir("./")
    if err != nil {
        log.Fatal(err)
    }

    for _, f := range files {
            fmt.Println(f.Name())
    }
}

Answer 6

Even simpler, use path/filepath:

package main    

import (
    "fmt"
    "log"
    "path/filepath"
)

func main() {
    files, err := filepath.Glob("*")
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(files) // contains a list of all files in the current directory
}