command-line-flags.go

package main

// Go provides a flag package supporting basic command-line flag parsing. We’ll use this package to implement our example command-line program.
import "flag"
import "fmt"

func main() {
	// Basic flag declarations are available for string, integer, and boolean options. Here we declare a string flag word with a default value "foo" and a short description. This flag.String function returns a string pointer (not a string value); we’ll see how to use this pointer below.
	wordPtr := flag.String("word", "foo", "a string")
	// This declares numb and fork flags, using a similar approach to the word flag.
	numbPtr := flag.Int("numb", 42, "an int")
	boolPtr := flag.Bool("fork", false, "a bool")
	// It’s also possible to declare an option that uses an existing var declared elsewhere in the program. Note that we need to pass in a pointer to the flag declaration function.
	var svar string
	flag.StringVar(&svar, "svar", "bar", "a string var")
	// Once all flags are declared, call flag.Parse() to execute the command-line parsing.
	flag.Parse()
	// Here we’ll just dump out the parsed options and any trailing positional arguments. Note that we need to dereference the pointers with e.g. *wordPtr to get the actual option values.
	fmt.Println("word:", *wordPtr)
	fmt.Println("numb:", *numbPtr)
	fmt.Println("fork:", *boolPtr)
	fmt.Println("svar:", svar)
	fmt.Println("tail:", flag.Args())
}