flag.Bool() Function in Golang With Examples

Go language provides inbuilt support for command-line parsing and has functions that could be used to define flags to be used with a command-line program using the flag package. This package provides the flag.Bool() function which is used to define a boolean flag with the specified name, default value, and usage string.

Syntax:

func Bool(name string, value bool, usage string) *bool

Parameters: This function accepts three parameters as mentioned above and described below:

• name: It is a string that specifies the name to be used for the flag.
• value: It is a boolean value that specifies the default value to be used by the flag.
• usage: It is a string that specifies the usage or help message to be shown for the flag.

Return Value: It returns an address of the boolean variable that stores the value of the flag defined.

Below programs illustrate the flag.Bool() function:

Example 1:

// Golang program to illustrate
// the flag.Bool() Function
package main

import (
    "flag"
    "fmt"
)

func main() {
    // Define a bool flag
    boolArgPtr := flag.Bool("arg1", false, "This is a bool argument")

    // Parse command line
    // into the defined flags
    flag.Parse()

    fmt.Println("Bool Arg:", *boolArgPtr)
}

Output:

• Specifying the flag value

  $ go run ex1.go -arg1=true
  Bool Arg: true

• Not specifying the flag value (Default Value)

  $ go run ex1.go
  Bool Arg: false
  

Example 2:

// Golang program to illustrate
// the flag.Bool() Function
package main

import (
    "flag"
    "fmt"
)

func main() {

    // Define multiple bool arguments
    plainArgPtr := flag.Bool("plaintext", false, "Enable plaintext")
    jsonArgPtr := flag.Bool("json", false, "Enable JSON")
    csvArgPtr := flag.Bool("csv", false, "Enable CSV")

    // Parse command line into the defined flags
    flag.Parse()

    fmt.Println("Enable plaintext:", *plainArgPtr)
    fmt.Println("Enable JSON:", *jsonArgPtr)
    fmt.Println("Enable CSV:", *csvArgPtr)
}

Output

• Specifying some flag values

  $ go run ex2.go -plaintext=true -csv=true
  Enable plaintext: true
  Enable JSON: false
  Enable CSV: true
  

• Not specifying any flag value (Default Values)

  $ go run ex2.go
  Enable plaintext: false
  Enable JSON: false
  Enable CSV: false