flags.go

package main

import (
	"flag"
	"fmt"
)

/*
Command-line flags are a common way to specify options for command-line programs.
For example, in wc -l the -l is a command-line flag.
*/

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

	// To experiment with the command-line flags program
	// it’s best to first compile it and then run the resulting binary directly.

}