How to Get correct file base name in Golang

Created Feb 14, 2023 at 19:58

Modified Feb 14, 2023 at 20:02

Using filepath.Base

The number is the index of the last slash in the string. If you want to get the file's base name, use filepath.Base:

package main

import (
  "fmt"
  "path/filepath"
)

func main() {

  path := "a/b.c.go"
  fmt.Println(filepath.Base(path)) // b.c.go

}

$ go run main.go
b.c.go

Using filepath.Split

Split splits path immediately following the final Separator, separating it into a directory and file name component.

package main

import (
  "fmt"
  "path/filepath"
)

func main() {

  path := "a/b.c.go"
  _, file := filepath.Split(path)
  fmt.Println(file) // b.c.go

}

$ go run main.go
b.c.go

The basename Function

The basename function below was inspired by the Unix shell utility of the same name. In our version, basename(s) removes any prefix of s that looks like a file system path with com- ponents separated by slashes, and it removes any suffix that looks like a file type:

package main

import (
  "fmt"
)

func main() {

  fmt.Println(basename("a/b.c.go")) // b.c
  fmt.Println(basename("a.c.go"))   // a.c
  fmt.Println(basename("abc"))      // abc

}

// basename removes directory components and a .suffix.
// e.g., a => a, a.go => a, a/b/c.go => c, a/b.c.go => b.c
func basename(s string) string {
  // Discard last '/' and everything before.
  for i := len(s) - 1; i >= 0; i-- {
    if s[i] == '/' {
      s = s[i+1:]
      break
    }
  }
  // Preserve everything before last '.'.
  for i := len(s) - 1; i >= 0; i-- {
    if s[i] == '.' {
      s = s[:i]
      break
    }
  }
  return s
}

$ go run main.go
b.c
a.c
abc

A simpler version uses the strings.LastIndex library function:

package main

import (
  "fmt"
  "strings"
)

func main() {

  fmt.Println(basename("a/b.c.go")) // b.c
  fmt.Println(basename("a.c.go"))   // a.c
  fmt.Println(basename("abc"))      // abc

}

func basename(s string) string {
  slash := strings.LastIndex(s, "/") // -1 if "/" not found
  s = s[slash+1:]
  if dot := strings.LastIndex(s, "."); dot >= 0 {
    s = s[:dot]
  }
  return s
}