如何将filemode转换为int？

Sample code:

func main() {
    p, _ := os.Open(os.Args[1])
    m, _ := p.Stat()
    println(m.Mode().Perm())
}

File has mode 0775 (-rwxrwxr-x). Running it like:

./main main

Prints 509

And second:

func main() {
    p, _ := os.Open(os.Args[1])
    m, _ := p.Stat()
    println(m.Mode().Perm().String())
}

This code prints -rwxrwxr-x.

How I can get mode in format 0775?

The value 509 is the decimal (base 10) representation of the permission bits.

The form 0775 is the octal representation (base 8). You can print a number in octal representation using the %o verb:

perm := 509
fmt.Printf("%o", perm)

Output (try it on the Go Playground):

775

If you want the output to be 4 digits (with a leading 0 in this case), use the format string "%04o":

fmt.Printf("%04o", perm) // Output: 0775