On Unix:
baz.js
dev.txt
todo.txt
Clean returns the shortest path name equivalent to path
by purely lexical processing. It applies the following rules
iteratively until no further processing can be done:
Replace multiple Separator elements with a single one.
Eliminate each . path name element (the current directory).
Eliminate each inner .. path name element (the parent directory)
along with the non-.. element that precedes it.
Eliminate .. elements that begin a rooted path:
that is, replace "/.." by "/" at the beginning of a path,
assuming Separator is '/'.
The returned path ends in a slash only if it represents a root directory,
such as "/" on Unix or `C:\` on Windows.
Finally, any occurrences of slash are replaced by Separator.
If the result of this process is an empty string, Clean
returns the string ".".
On Windows, Clean does not modify the volume name other than to replace
occurrences of "/" with `\`.
For example, Clean("//host/share/../x") returns `\\host\share\x`.
See also Rob Pike, “Lexical File Names in Plan 9 or
Getting Dot-Dot Right,”
https://9p.io/sys/doc/lexnames.html
func Dir(path string) string
Dir returns all but the last element of path, typically the path's directory.
After dropping the final element, Dir calls Clean on the path and trailing
slashes are removed.
If the path is empty, Dir returns ".".
If the path consists entirely of separators, Dir returns a single separator.
The returned path does not end in a separator unless it is the root directory.
package main
import (
"fmt"
"path/filepath"
func main() {
fmt.Println("On Unix:")
fmt.Println(filepath.Dir("/foo/bar/baz.js"))
fmt.Println(filepath.Dir("/foo/bar/baz"))
fmt.Println(filepath.Dir("/foo/bar/baz/"))
fmt.Println(filepath.Dir("/dirty//path///"))
fmt.Println(filepath.Dir("dev.txt"))
fmt.Println(filepath.Dir("../todo.txt"))
fmt.Println(filepath.Dir(".."))
fmt.Println(filepath.Dir("."))
fmt.Println(filepath.Dir("/"))
fmt.Println(filepath.Dir(""))
Output:
On Unix:
/foo/bar
/foo/bar
/foo/bar/baz
/dirty/path
func EvalSymlinks(path string) (string, error)
EvalSymlinks returns the path name after the evaluation of any symbolic
links.
If path is relative the result will be relative to the current directory,
unless one of the components is an absolute symbolic link.
EvalSymlinks calls Clean on the result.
Ext returns the file name extension used by path.
The extension is the suffix beginning at the final dot
in the final element of path; it is empty if there is
no dot.
package main
import (
"fmt"
"path/filepath"
func main() {
fmt.Printf("No dots: %q\n", filepath.Ext("index"))
fmt.Printf("One dot: %q\n", filepath.Ext("index.js"))
fmt.Printf("Two dots: %q\n", filepath.Ext("main.test.js"))
Output:
No dots: ""
One dot: ".js"
Two dots: ".js"
func FromSlash(path string) string
FromSlash returns the result of replacing each slash ('/') character
in path with a separator character. Multiple slashes are replaced
by multiple separators.
See also the Localize function, which converts a slash-separated path
as used by the io/fs package to an operating system path.
func Glob(pattern string) (matches []string, err error)
Glob returns the names of all files matching pattern or nil
if there is no matching file. The syntax of patterns is the same
as in Match. The pattern may describe hierarchical names such as
/usr/*/bin/ed (assuming the Separator is '/').
Glob ignores file system errors such as I/O errors reading directories.
The only possible returned error is ErrBadPattern, when pattern
is malformed.
func HasPrefix(p, prefix string) bool
HasPrefix exists for historical compatibility and should not be used.
Deprecated: HasPrefix does not respect path boundaries and
does not ignore case when required.
fmt.Println("On Unix:")
fmt.Println(filepath.IsAbs("/home/gopher"))
fmt.Println(filepath.IsAbs(".bashrc"))
fmt.Println(filepath.IsAbs(".."))
fmt.Println(filepath.IsAbs("."))
fmt.Println(filepath.IsAbs("/"))
fmt.Println(filepath.IsAbs(""))
Output:
On Unix:
false
false
false
false
func IsLocal(path string) bool
IsLocal reports whether path, using lexical analysis only, has all of these properties:
is within the subtree rooted at the directory in which path is evaluated
is not an absolute path
is not empty
on Windows, is not a reserved name such as "NUL"
If IsLocal(path) returns true, then
Join(base, path) will always produce a path contained within base and
Clean(path) will always produce an unrooted path with no ".." path elements.
IsLocal is a purely lexical operation.
In particular, it does not account for the effect of any symbolic links
that may exist in the filesystem.
func Join(elem ...string) string
Join joins any number of path elements into a single path,
separating them with an OS specific Separator. Empty elements
are ignored. The result is Cleaned. However, if the argument
list is empty or all its elements are empty, Join returns
an empty string.
On Windows, the result will only be a UNC path if the first
non-empty element is a UNC path.
package main
import (
"fmt"
"path/filepath"
func main() {
fmt.Println("On Unix:")
fmt.Println(filepath.Join("a", "b", "c"))
fmt.Println(filepath.Join("a", "b/c"))
fmt.Println(filepath.Join("a/b", "c"))
fmt.Println(filepath.Join("a/b", "/c"))
fmt.Println(filepath.Join("a/b", "../../../xyz"))
Output:
On Unix:
a/b/c
a/b/c
a/b/c
a/b/c
../xyz
func Localize(path string) (string, error)
Localize converts a slash-separated path into an operating system path.
The input path must be a valid path as reported by io/fs.ValidPath.
Localize returns an error if the path cannot be represented by the operating system.
For example, the path a\b is rejected on Windows, on which \ is a separator
character and cannot be part of a filename.
The path returned by Localize will always be local, as reported by IsLocal.
func Match(pattern, name string) (matched bool, err error)
Match reports whether name matches the shell file name pattern.
The pattern syntax is:
pattern:
{ term }
term:
'*' matches any sequence of non-Separator characters
'?' matches any single non-Separator character
'[' [ '^' ] { character-range } ']'
character class (must be non-empty)
c matches character c (c != '*', '?', '\\', '[')
'\\' c matches character c
character-range:
c matches character c (c != '\\', '-', ']')
'\\' c matches character c
lo '-' hi matches character c for lo <= c <= hi
Match requires pattern to match all of name, not just a substring.
The only possible returned error is ErrBadPattern, when pattern
is malformed.
On Windows, escaping is disabled. Instead, '\\' is treated as
path separator.
package main
import (
"fmt"
"path/filepath"
func main() {
fmt.Println("On Unix:")
fmt.Println(filepath.Match("/home/catch/*", "/home/catch/foo"))
fmt.Println(filepath.Match("/home/catch/*", "/home/catch/foo/bar"))
fmt.Println(filepath.Match("/home/?opher", "/home/gopher"))
fmt.Println(filepath.Match("/home/\\*", "/home/*"))
Output:
On Unix:
true <nil>
false <nil>
true <nil>
true <nil>
func Rel(basepath, targpath string) (string, error)
Rel returns a relative path that is lexically equivalent to targpath when
joined to basepath with an intervening separator. That is,
Join(basepath, Rel(basepath, targpath)) is equivalent to targpath itself.
On success, the returned path will always be relative to basepath,
even if basepath and targpath share no elements.
An error is returned if targpath can't be made relative to basepath or if
knowing the current working directory would be necessary to compute it.
Rel calls Clean on the result.
package main
import (
"fmt"
"path/filepath"
func main() {
paths := []string{
"/a/b/c",
"/b/c",
"./b/c",
base := "/a"
fmt.Println("On Unix:")
for _, p := range paths {
rel, err := filepath.Rel(base, p)
fmt.Printf("%q: %q %v\n", p, rel, err)
Output:
On Unix:
"/a/b/c": "b/c" <nil>
"/b/c": "../b/c" <nil>
"./b/c": "" Rel: can't make ./b/c relative to /a
func Split(path string) (dir, file string)
Split splits path immediately following the final Separator,
separating it into a directory and file name component.
If there is no Separator in path, Split returns an empty dir
and file set to path.
The returned values have the property that path = dir+file.
package main
import (
"fmt"
"path/filepath"
func main() {
paths := []string{
"/home/arnie/amelia.jpg",
"/mnt/photos/",
"rabbit.jpg",
"/usr/local//go",
fmt.Println("On Unix:")
for _, p := range paths {
dir, file := filepath.Split(p)
fmt.Printf("input: %q\n\tdir: %q\n\tfile: %q\n", p, dir, file)
Output:
On Unix:
input: "/home/arnie/amelia.jpg"
dir: "/home/arnie/"
file: "amelia.jpg"
input: "/mnt/photos/"
dir: "/mnt/photos/"
file: ""
input: "rabbit.jpg"
dir: ""
file: "rabbit.jpg"
input: "/usr/local//go"
dir: "/usr/local//"
file: "go"
func SplitList(path string) []string
SplitList splits a list of paths joined by the OS-specific ListSeparator,
usually found in PATH or GOPATH environment variables.
Unlike strings.Split, SplitList returns an empty slice when passed an empty
string.
package main
import (
"fmt"
"path/filepath"
func main() {
fmt.Println("On Unix:", filepath.SplitList("/a/b/c:/usr/bin"))
Output:
On Unix: [/a/b/c /usr/bin]
func ToSlash(path string) string
ToSlash returns the result of replacing each separator character
in path with a slash ('/') character. Multiple separators are
replaced by multiple slashes.
VolumeName returns leading volume name.
Given "C:\foo\bar" it returns "C:" on Windows.
Given "\\host\share\foo" it returns "\\host\share".
On other platforms it returns "".
func Walk(root string, fn WalkFunc) error
Walk walks the file tree rooted at root, calling fn for each file or
directory in the tree, including root.
All errors that arise visiting files and directories are filtered by fn:
see the WalkFunc documentation for details.
The files are walked in lexical order, which makes the output deterministic
but requires Walk to read an entire directory into memory before proceeding
to walk that directory.
Walk does not follow symbolic links.
Walk is less efficient than WalkDir, introduced in Go 1.16,
which avoids calling os.Lstat on every visited file or directory.
//go:build !windows && !plan9
package main
import (
"fmt"
"io/fs"
"path/filepath"
func prepareTestDirTree(tree string) (string, error) {
tmpDir, err := os.MkdirTemp("", "")
if err != nil {
return "", fmt.Errorf("error creating temp directory: %v\n", err)
err = os.MkdirAll(filepath.Join(tmpDir, tree), 0755)
if err != nil {
os.RemoveAll(tmpDir)
return "", err
return tmpDir, nil
func main() {
tmpDir, err := prepareTestDirTree("dir/to/walk/skip")
if err != nil {
fmt.Printf("unable to create test dir tree: %v\n", err)
return
defer os.RemoveAll(tmpDir)
os.Chdir(tmpDir)
subDirToSkip := "skip"
fmt.Println("On Unix:")
err = filepath.Walk(".", func(path string, info fs.FileInfo, err error) error {
if err != nil {
fmt.Printf("prevent panic by handling failure accessing a path %q: %v\n", path, err)
return err
if info.IsDir() && info.Name() == subDirToSkip {
fmt.Printf("skipping a dir without errors: %+v \n", info.Name())
return filepath.SkipDir
fmt.Printf("visited file or dir: %q\n", path)
return nil
if err != nil {
fmt.Printf("error walking the path %q: %v\n", tmpDir, err)
return
Output:
On Unix:
visited file or dir: "."
visited file or dir: "dir"
visited file or dir: "dir/to"
visited file or dir: "dir/to/walk"
skipping a dir without errors: skip
func WalkDir(root string, fn fs.WalkDirFunc) error
WalkDir walks the file tree rooted at root, calling fn for each file or
directory in the tree, including root.
All errors that arise visiting files and directories are filtered by fn:
see the fs.WalkDirFunc documentation for details.
The files are walked in lexical order, which makes the output deterministic
but requires WalkDir to read an entire directory into memory before proceeding
to walk that directory.
WalkDir does not follow symbolic links.
WalkDir calls fn with paths that use the separator character appropriate
for the operating system. This is unlike io/fs.WalkDir, which always
uses slash separated paths.
type WalkFunc func(path string, info fs.FileInfo, err error) error
WalkFunc is the type of the function called by Walk to visit each
file or directory.
The path argument contains the argument to Walk as a prefix.
That is, if Walk is called with root argument "dir" and finds a file
named "a" in that directory, the walk function will be called with
argument "dir/a".
The directory and file are joined with Join, which may clean the
directory name: if Walk is called with the root argument "x/../dir"
and finds a file named "a" in that directory, the walk function will
be called with argument "dir/a", not "x/../dir/a".
The info argument is the fs.FileInfo for the named path.
The error result returned by the function controls how Walk continues.
If the function returns the special value SkipDir, Walk skips the
current directory (path if info.IsDir() is true, otherwise path's
parent directory). If the function returns the special value SkipAll,
Walk skips all remaining files and directories. Otherwise, if the function
returns a non-nil error, Walk stops entirely and returns that error.
The err argument reports an error related to path, signaling that Walk
will not walk into that directory. The function can decide how to
handle that error; as described earlier, returning the error will
cause Walk to stop walking the entire tree.
Walk calls the function with a non-nil err argument in two cases.
First, if an os.Lstat on the root directory or any directory or file
in the tree fails, Walk calls the function with path set to that
directory or file's path, info set to nil, and err set to the error
from os.Lstat.
Second, if a directory's Readdirnames method fails, Walk calls the
function with path set to the directory's path, info, set to an
fs.FileInfo describing the directory, and err set to the error from
Readdirnames.
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