Golang : untar or extract tar ball archive example

Many system administrators like to use the tar program to archive the entire directory and gzip to compress newly created tar ball for backup purpose or FTP to another server for batch processing purpose.

There are times when a program sitting on one server will receive tar balls from another or multiple servers. The 'traditional' way is to untar the files with shell scripts and then process the untarred files. Since this tutorial focus on is on Golang, we will explore how to untar the compressed tar ball with Golang.

The codes below will demonstrate how to untar files with Golang.

go-untar.go

 package main

 import (
 "archive/tar"
 "compress/gzip"
 "flag"
 "fmt"
 "io"
 "os"
 "strings"
 )

 func main() {

 flag.Parse() // get the arguments from command line

 sourcefile := flag.Arg(0)

 if sourcefile == "" {
 fmt.Println("Usage : go-untar sourcefile.tar")
 os.Exit(1)
 }

 file, err := os.Open(sourcefile)

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 defer file.Close()

 var fileReader io.ReadCloser = file

 // just in case we are reading a tar.gz file, add a filter to handle gzipped file
 if strings.HasSuffix(sourcefile, ".gz") {
 if fileReader, err = gzip.NewReader(file); err != nil {

 fmt.Println(err)
 os.Exit(1)
 }
 defer fileReader.Close()
 }

 tarBallReader := tar.NewReader(fileReader)

 // Extracting tarred files

 for {
 header, err := tarBallReader.Next()
 if err != nil {
 if err == io.EOF {
 break
 }
 fmt.Println(err)
 os.Exit(1)
 }

 // get the individual filename and extract to the current directory
 filename := header.Name

 switch header.Typeflag {
 case tar.TypeDir:
 // handle directory
 fmt.Println("Creating directory :", filename)
 err = os.MkdirAll(filename, os.FileMode(header.Mode)) // or use 0755 if you prefer

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 case tar.TypeReg:
 // handle normal file
 fmt.Println("Untarring :", filename)
 writer, err := os.Create(filename)

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 io.Copy(writer, tarBallReader)

 err = os.Chmod(filename, os.FileMode(header.Mode))

 if err != nil {
 fmt.Println(err)
 os.Exit(1)
 }

 writer.Close()
 default:
 fmt.Printf("Unable to untar type : %c in file %s", header.Typeflag, filename)
 }
 }

 }

Sample output :

./go-untar testdir.tar (non gzip)

Creating directory : ./testdir/

Untarring : ./testdir/dumb3.txt

---

./go-untar testdir.tar.gz

Creating directory : ./testdir/

Untarring : ./testdir/dumb3.txt