Command-Line Flag Parsing in Golang

Introduction

The purpose of this challenge is to implement a command-line program that supports basic command-line flag parsing using the flag package in Golang.

Skills Graph

Command-line flags

Implement a Golang program that parses command-line flags and outputs the parsed options and any trailing positional arguments. The program should support the following flags:

• word: a string flag with a default value of "foo".
• numb: an integer flag with a default value of 42.
• fork: a boolean flag with a default value of false.
• svar: a string flag that uses an existing variable declared elsewhere in the program.

Requirements

• The program should use the flag package to parse command-line flags.
• The program should output the parsed options and any trailing positional arguments.
• The program should support the word, numb, fork, and svar flags as described above.

Example

## To experiment with the command-line flags program it's
## best to first compile it and then run the resulting
## binary directly.
$ go build command-line-flags.go

## Try out the built program by first giving it values for
## all flags.
$ ./command-line-flags -word=opt -numb=7 -fork -svar=flag
word: opt
numb: 7
fork: true
svar: flag
tail: []

## Note that if you omit flags they automatically take
## their default values.
$ ./command-line-flags -word=opt
word: opt
numb: 42
fork: false
svar: bar
tail: []

## Trailing positional arguments can be provided after
## any flags.
$ ./command-line-flags -word=opt a1 a2 a3
word: opt
...
tail: [a1 a2 a3]

## Note that the `flag` package requires all flags to
## appear before positional arguments (otherwise the flags
## will be interpreted as positional arguments).
$ ./command-line-flags -word=opt a1 a2 a3 -numb=7
word: opt
numb: 42
fork: false
svar: bar
tail: [a1 a2 a3 -numb=7]

## Use `-h` or `--help` flags to get automatically
## generated help text for the command-line program.
$ ./command-line-flags -h
Usage of ./command-line-flags:
-fork=false: a bool
-numb=42: an int
-svar="bar": a string var
-word="foo": a string

## If you provide a flag that wasn't specified to the
## `flag` package, the program will print an error message
## and show the help text again.
$ ./command-line-flags -wat
flag provided but not defined: -wat
Usage of ./command-line-flags:
...

Summary

In this challenge, we learned how to use the flag package in Golang to parse command-line flags. We implemented a program that supports basic flag parsing and outputs the parsed options and any trailing positional arguments.