Samarthya

In the last blog I talked about command line arguments os.Args[]. In this I will try and create a sample banner program that shall

• Take 3 arguments
• n – Number of times a message has to be repeated.
• m – The message that needs to be shown.
• d – If debug message needs to be shown.

I am going to use the flags package.

Defining: Banner

The package flag has the extended capability of parsing the flags.

Define Flags

Variant one

var times = flag.Int("n", 1, "number of times the message needs to be displayed")
var msg = flag.String("m", "", "the message that needs to be printed")
var dbg = flag.Bool("d", false, "to debug or not")

You can also define flags using

var nTimes int

func init() {
	flag.IntVar(&nTimes, "n", 1, "number of times the message needs to be displayed")
}

After all flags are defined you must call, to parse the command line into flags. If you miss this one you might not get the desired results. (Give it a try)

// Must be called after all flags are defined and before flags are accessed within the program
flag.Parse()

How to pass values to these flags?

-flag
-flag=x
-flag x

Build

go build src/cmdline/cmd.go

This will produce the binary – cmd.

Run the cmd

./cmd
  -d    to debug or not
  -m string
        the message that needs to be printed
  -n int
        number of times the message needs to be displayed (default 1)

./cmd -n 2 -m="Why is world round?"

--- Command line Program ---

 >> Why is world round?

 >> Why is world round?

./cmd -n 2 -m="Why is world round?" -d=true
DBG: Number of Arguments: 5
--- Command line Program ---

 >> Why is world round?

 >> Why is world round?

./cmd -m="Why is world round?" -n=3  -d=true
DBG: Number of Arguments: 4
--- Command line Program ---

 >> Why is world round?

 >> Why is world round?

 >> Why is world round?