How to redirect stderr to file

[pradeek_k]

I’m trying to rediect standardout and standarderr to file, I can redirect standard out to file by overwriting

os.Stdout = *os.File

But when I’m trying to do the same with os.Stderr its not taking in effect, errors and other panics are still printing in console.

[skillian (Sean Killian)]

Can you redirect stderr and stdout from wherever you start your go program instead of within the Go program? E.g.:

./mygoprogram > /var/log/mygoprogram.stdout.log 2> /var/log/mygoprogram.stderr.log

[pradeek_k]

So I need to write a bash program to automate this process?

[skillian (Sean Killian)]

I’m not saying it’s your only option, just that it seems like a better option than changing os.Stdout and/or os.Stderr. There might be some initialization in some package somewhere that caches the value of os.Stdout before you change it; for example:

package "somepackage"

var someKindOfLogger = &logger{
    writer: os.Stderr,
    // ...
}

func logSomethingOnPanic() {
    someKindOfLogger.WriteSomething() // uses someKindOfLogger.writer which is
        // the value of os.Stderr before you changed it.
}

package "main"

func main() {
    os.Stderr = createStderrReplacementFile() // this doesn't help because other
        // init code already cached the value of os.Stderr somewhere.
    doSomethingThatPanics()
}

If you redirect stderr and stdout, there is no timing issue related to changing os.Stdout before or after it’s been cached somewhere.