What’s Go’s equivalent of argv[0]?

Question

import "os"
os.Args[0] // name of the command that it is running as
os.Args[1] // first command line parameter, ...

Arguments are exposed in the os package http://golang.org/pkg/os/#Variables

If you’re going to do argument handling, the flag package http://golang.org/pkg/flag is the preferred way. Specifically for your case flag.Usage

Update for the example you gave:

func usage() {
    fmt.Fprintf(os.Stderr, "usage: %s [inputfile]\n", os.Args[0])
    flag.PrintDefaults()
    os.Exit(2)
}

should do the trick