⌛ Temporary file in Go - how to create?

When you write a program that processes large amounts of data, or you test a program that creates files, you often need the ability to create temporary files that allow you to store your data for a short time without cluttering your project’s disk space. In Go, you can create a temporary file with os.CreateTemp() function and a temporary directory with os.MkdirTemp() function.

os.CreateTemp() and os.MkdirTemp() are available since Go 1.17. For older versions you can use ioutil.TempFile() and ioutil.TempDir().

Create a temporary file

package main

import (
    "log"
    "os"
)

func main() {
    // create and open a temporary file
    f, err := os.CreateTemp("", "tmpfile-") // in Go version older than 1.17 you can use ioutil.TempFile
    if err != nil {
        log.Fatal(err)
    }

    // close and remove the temporary file at the end of the program
    defer f.Close()
    defer os.Remove(f.Name())

    // write data to the temporary file
    data := []byte("abc abc abc")
    if _, err := f.Write(data); err != nil {
        log.Fatal(err)
    }
}

The function func CreateTemp(dir, pattern string) (*File, error) has two parameters:

• dir which is a directory where a temporary file should be created. If left empty, the default directory for temporary files (for a given OS) is used.
• pattern that is used to generate names of temporary files. The name is created by appending a random string to the end of the pattern. In this way, in the example, we get names such as tmpfile-483140887. You can also use * to indicate where the random string should be placed. Giving tmpfile-*.txt you get, for example, tmpfile-483140887.txt.

If you don’t use the temporary file anymore, it is a good practice to remove it using os.Remove().

Create a temporary directory

package main

import (
    "fmt"
    "log"
    "os"
)

func main() {
    // create a temporary directory
    name, err := os.MkdirTemp("", "dir") // in Go version older than 1.17 you can use ioutil.TempDir
    if err != nil {
        log.Fatal(err)
    }

    // remove the temporary directory at the end of the program
    defer os.RemoveAll(name)

    // print path of the directory
    fmt.Println(name)
}

Parameters of the func MkdirTemp(dir, pattern string) (string, error) function work the same way as in the case of os.CreateTemp(). As before, after you finish working with the temporary folder, you should remember to delete it, for example, via os.RemoveAll.