How can I compare two files in golang?

Question

With Python I can do the next:

equals = filecmp.cmp(file_old, file_new)

Is there any builtin function to do that in go language? I googled it but without success.

I could use some hash function in hash/crc32 package, but that is more work that the above Python code.

Answer 1

To complete the @captncraig answer, if you want to know if the two files are the same, you can use the SameFile(fi1, fi2 FileInfo) method from the OS package.

SameFile reports whether fi1 and fi2 describe the same file. For example, on Unix this means that the device and inode fields of the two underlying structures are identical;

Otherwise, if you want to check the files contents, here is a solution which checks the two files line by line avoiding the load of the entire files in memory.

First try: https://play.golang.org/p/NlQZRrW1dT

---

EDIT: Read by bytes chunks and fail fast if the files have not the same size. https://play.golang.org/p/YyYWuCRJXV

const chunkSize = 64000

func deepCompare(file1, file2 string) bool {
    // Check file size ...

    f1, err := os.Open(file1)
    if err != nil {
        log.Fatal(err)
    }
    defer f1.Close()

    f2, err := os.Open(file2)
    if err != nil {
        log.Fatal(err)
    }
    defer f2.Close()

    for {
        b1 := make([]byte, chunkSize)
        _, err1 := f1.Read(b1)

        b2 := make([]byte, chunkSize)
        _, err2 := f2.Read(b2)

        if err1 != nil || err2 != nil {
            if err1 == io.EOF && err2 == io.EOF {
                return true
            } else if err1 == io.EOF || err2 == io.EOF {
                return false
            } else {
                log.Fatal(err1, err2)
            }
        }

        if !bytes.Equal(b1, b2) {
            return false
        }
    }
}