- a hint on how to compare two files. The recipe will show you how to quickly determine whether the files are identical. The recipe will also present you with a way to find differences between the two.
Create the comparison.go file with the following content:#
package main
import (
"bufio"
"crypto/md5"
"fmt"
"io"
"os"
)
var data = []struct {
name string
cont string
perm os.FileMode
}{
{"test1.file", "Hello\nGolang is great", 0666},
{"test2.file", "Hello\nGolang is great", 0666},
{"test3.file", "Not matching\nGolang is great\nLast line",
0666},
}
func main() {
files := []*os.File{}
for _, fData := range data {
f, err := os.Create(fData.name)
if err != nil {
panic(err)
}
defer f.Close()
_, err = io.WriteString(f, fData.cont)
if err != nil {
panic(err)
}
files = append(files, f)
}
// Compare by checksum
checksums := []string{}
for _, f := range files {
f.Seek(0, 0) // reset to beginning of file
sum, err := getMD5SumString(f)
if err != nil {
panic(err)
}
checksums = append(checksums, sum)
}
fmt.Println("### Comparing by checksum ###")
compareCheckSum(checksums[0], checksums[1])
compareCheckSum(checksums[0], checksums[2])
fmt.Println("### Comparing line by line ###")
files[0].Seek(0, 0)
files[2].Seek(0, 0)
compareFileByLine(files[0], files[2])
// Cleanup
for _, val := range data {
os.Remove(val.name)
}
}
func getMD5SumString(f *os.File) (string, error) {
file1Sum := md5.New()
_, err := io.Copy(file1Sum, f)
if err != nil {
return "", err
}
return fmt.Sprintf("%X", file1Sum.Sum(nil)), nil
}
func compareCheckSum(sum1, sum2 string) {
match := "match"
if sum1 != sum2 {
match = " does not match"
}
fmt.Printf("Sum: %s and Sum: %s %s\n", sum1, sum2, match)
}
func compareLines(line1, line2 string) {
sign := "o"
if line1 != line2 {
sign = "x"
}
fmt.Printf("%s | %s | %s \n", sign, line1, line2)
}
func compareFileByLine(f1, f2 *os.File) {
sc1 := bufio.NewScanner(f1)
sc2 := bufio.NewScanner(f2)
for {
sc1Bool := sc1.Scan()
sc2Bool := sc2.Scan()
if !sc1Bool && !sc2Bool {
break
}
compareLines(sc1.Text(), sc2.Text())
}
}
output:
sangam:golang-daily sangam$ go run comparison.go
### Comparing by checksum ###
Sum: 5A07C1538087CD5B5C365DE52970E0A3 and Sum: 5A07C1538087CD5B5C365DE52970E0A3 match
Sum: 5A07C1538087CD5B5C365DE52970E0A3 and Sum: FED2EADA5D1D1EBF745DFDC7D1385E6C does not match
### Comparing line by line ###
x | Hello | Not matching
o | Golang is great | Golang is great
x | | Last line
sangam:golang-daily sangam$
How it works...#
-
The comparison of the two files can be done in a few ways. This recipe describes the two basic ones. The first one is by doing a comparison of the whole file by creating the checksum of the file.
-
The Generating checksum recipe of (https://gopherlabs.kubedaily.com/Beginners/Generating_checksums.html) Dealing with Numbers shows how you can create the checksum of the file. This way, the getMD5SumString function generates the checksum string, which is a hexadecimal representation of the byte result of MD5. The strings are then compared.
-
The second approach compares the files line by line (in this case, the string content).
-
In case the lines are not matching, the x sign is included. This is the same way you can compare the binary content, but you will need to scan the file by blocks of bytes (byte slices).