Go provides a flag package to handle command-line flags.
Go flags vary slightly from traditional unix flags.
Go has no “short” and “long” flags differentiated by one or two dashes.
-debug is the same as --debug, and the three options -a -d -v may not be written -adv.
Giving values to flags works like -level=2 or -level 2 (except that boolean values must use the = form to avoid ambiguity with shell wildcards).
Flag parsing stops just before the first non-flag argument (- is a non-flag argument) or after the terminator --.
Specify one or more flag variables, then call flag.Parse().
import "flag"
var ip = flag.Int("flagname", 1234, "help message for flagname")
func init() {
flag.Parse()
fmt.Println(*ip)
}
…or:
var flagvar int
func init() {
flag.IntVar(&flagvar, "flagname", 1234, "help message for flagname")
flag.Parse()
fmt.Println(flagvar)
}
The FlagSet types enables subcommands (e.g., git log or ip address show).
package main
import (
"flag"
"fmt"
"os"
)
func main() {
var a, b, y, z string
// Set of flags for subcommand 1
fs1 := flag.NewFlagSet("fs1", flag.ExitOnError)
fs1.StringVar(&a, "a", "foo", "subcommand 1 flag 'a'")
fs1.StringVar(&b, "b", "bar", "subcommand 1 flag 'b'")
// Set of flags for subcommand 2
fs2 := flag.NewFlagSet("fs2", flag.ExitOnError)
fs2.StringVar(&y, "y", "foo", "subcommand 2 flag 'y'")
fs2.StringVar(&z, "z", "bar", "subcommand 2 flag 'z'")
help := "Add the subcommand 'edit' or 'list'!"
// Switch on subcommands, then apply the desired set of flags.
if len(os.Args) < 2 {
fmt.Fprintln(os.Stderr, help)
os.Exit(0)
}
switch os.Args[1] {
case "edit":
if err := fs1.Parse(os.Args[2:]); err == nil {
fmt.Println("edit", a)
}
case "list":
if err := fs2.Parse(os.Args[2:]); err == nil {
fmt.Println("list", z)
}
default:
fmt.Fprintln(os.Stderr, help)
os.Exit(0)
}
}