Exit with error code in go?

What's the idiomatic way to exit a program with some error code?

The documentation for Exit says "The program terminates immediately; deferred functions are not run.", and log.Fatal just calls Exit. For things that aren't heinous errors, terminating the program without running deferred functions seems extreme.

Am I supposed to pass around some state that indicate that there's been an error, and then call Exit(1) at some point where I know that I can exit safely, with all deferred functions having been run?

I do something along these lines in most of my real main packages, so that the return err convention is adopted as soon as possible, and has a proper termination:

func main() {
    if err := run(); err != nil {
        fmt.Fprintf(os.Stderr, "error: %v\n", err)
        os.Exit(1)
    }
}

func run() error {
    err := something()
    if err != nil {
        return err
    }
    // etc
}

In Python I commonly use a pattern, which being converted to Go looks like this:

func run() int {
	// here goes
	// the code

	return 1
}

func main() {
	os.Exit(run())
}

I think the most clear way to do it is to set the exitCode at the top of main, then defer closing as the next step. That lets you change exitCode anywhere in main, and it's last value will be exited with:

package main

import (
    "fmt"
    "os"
)

func main() {
    exitCode := 0
    defer func() { os.Exit(exitCode) }()

    // Do whatever, including deferring more functions

    defer func() {
        fmt.Printf("Do some cleanup\n")
    }()

    func() {
        fmt.Printf("Do some work\n")
    }()

    // But let's say something went wrong
    exitCode = 1

    // Do even more work/cleanup if you want
 
    // At the end, os.Exit will be called with the last value of exitCode
}

Output:

Do some work
Do some cleanup

Program exited: status 1.

Go Playgroundhttps://play.golang.org/p/AMUR4m_A9Dw

Note that an important disadvantage of this is that you don't exit the process as soon as you set the error code.

As mentioned by fas, you have func Exit(exitcode int) from the os package.

However, if you need the defered function to be applied, you always can use the defer keyword like this:

http://play.golang.org/p/U-hAS88Ug4

You perform all your operation, affect a error variable and at the very end, when everything is cleaned up, you can exit safely.

Otherwise, you could also use panic/recover:
http://play.golang.org/p/903e76GnQ-

When you have an error, you panic, end you cleanup where you catch (recover) it.

Yes, actually. The os package provides this.

package main

import "os"

func main() {
    os.Exit(1)
}

http://golang.org/pkg/os/#Exit

Edit: so it looks like you know of Exit. This article gives an overview of Panic which will let deferred functions run before returning. Using this in conjunction with an exit may be what you're looking for. http://blog.golang.org/defer-panic-and-recover

Another good way I follow is:

if err != nil {
    // log.Fatal will print the error message and will internally call System.exit(1) so the program will terminate
	log.Fatal("fatal error message")
}