As far as I know, you can't redirect the output from panic away from standard error, or to your logger. The best thing you can do is redirect standard error to a file which you can do externally, or inside your program.
For my rclone program I redirected standard error to capture everything to a file on an option which is unfortunately isn't particularly easy to do in a cross platform way. Here is how I did it (see the redirect*.go files)
For linux/unix
// Log the panic under unix to the log file
//+build unix
package main
import (
"log"
"os"
"syscall"
)
// redirectStderr to the file passed in
func redirectStderr(f *os.File) {
err := syscall.Dup2(int(f.Fd()), int(os.Stderr.Fd()))
if err != nil {
log.Fatalf("Failed to redirect stderr to file: %v", err)
}
}
and for windows
// Log the panic under windows to the log file
//
// Code from minix, via
//
// http://play.golang.org/p/kLtct7lSUg
//+build windows
package main
import (
"log"
"os"
"syscall"
)
var (
kernel32 = syscall.MustLoadDLL("kernel32.dll")
procSetStdHandle = kernel32.MustFindProc("SetStdHandle")
)
func setStdHandle(stdhandle int32, handle syscall.Handle) error {
r0, _, e1 := syscall.Syscall(procSetStdHandle.Addr(), 2, uintptr(stdhandle), uintptr(handle), 0)
if r0 == 0 {
if e1 != 0 {
return error(e1)
}
return syscall.EINVAL
}
return nil
}
// redirectStderr to the file passed in
func redirectStderr(f *os.File) {
err := setStdHandle(syscall.STD_ERROR_HANDLE, syscall.Handle(f.Fd()))
if err != nil {
log.Fatalf("Failed to redirect stderr to file: %v", err)
}
// SetStdHandle does not affect prior references to stderr
os.Stderr = f
}