How to Access File Group ID (GID) in Go?

Accessing File Group ID (GID) in Go

In Go, files can be queried for their metadata using the os.Stat() function, which returns a FileInfo object. This object provides information about the file, including its size, creation time, and permissions. However, retrieving the Group ID (GID) of a file can be challenging due to the opaque nature of the FileInfo object's Sys() method.

The Sys() method returns an Interface{} value that lacks any exposed methods. While it's possible to print the Sys() value to inspect it, the GID is not directly accessible.

Solution

To overcome this limitation, we can use the reflect module to determine the actual type underlying the Sys() value. On Linux, the system-dependent information returned by Sys() is commonly stored in the syscall.Stat_t struct.

<code class="go">import (
    "fmt"
    "os"
    "reflect"
    "syscall"
)

func main() {
    file_info, _ := os.Stat(abspath)
    file_sys := file_info.Sys()
    file_sys_t := reflect.ValueOf(file_sys).Elem()

    gid := file_sys_t.FieldByName("Gid").String()

    fmt.Println("File GID:", gid)
}</code>

By casting the file_sys value to a *syscall.Stat_t struct, we gain access to its fields, including the Gid field which contains the numeric group ID.

Note:

This solution is specific to Linux, as the system-dependent information returned by Sys() can vary across operating systems. For a portable solution, you may需要使用第三方库或更低级的系统调用来获取文件的 GID。

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