Parse strings like command line arguments with Go

How do I take a string and parse it as if it was a series of command line arguments? I want to be able to take a string and parse that with flag and/or pflag. How do I do this?

package main

import (
	"fmt"
	"os"

	flag "github.com/spf13/pflag"
)

func main() {
	command := `unimportant -fb "quoted string"`
	var (
		foo bool
		bar string
	)
	flag.BoolVarP(&foo, "foo", "f", false, "foo")
	flag.StringVarP(&bar, "bar", "b", "default", "bar")

	// Parse command
	os.Args = append(os.Args, "-fb", "quoted string")
	flag.Parse()

	fmt.Println(command)
	fmt.Println("foo", foo)
	fmt.Println("bar", bar)
}

The easiest way would be use the package shellwords to parse your string into an argv of shell words, and then use a command-line parser other than flag or pflag that supports parsing an arbitrary argv (say flags, but there are many to choose from.)

// Parse  your string into an []string as the shell would.

argv, err := shellwords.Parse("./foo --bar=baz")
// argv should be ["./foo", "--bar=baz"]

...

// define your options, etc. here

...

extraArgs, err := flags.ParseArgs(&opts, argv)

Regex can use to detect each argument. There are two possible forms for an argument:

1. a group of letters and a negative sign: [-a-zA-Z]+
2. something sandwiched between two ": ".*?"

Information about regexp package: https://pkg.go.dev/regexp

Information about regexp syntax: https://pkg.go.dev/regexp/syntax@go1.17.6

re := regexp.MustCompile(`([-a-zA-Z]+)|(".*?[^\\]")|("")`)
command := `unimportant -fb "quoted string"`

allArgs := re.FindAllString(command, -1)

//fmt.Printf("%+v\n", allArgs)

// to remove "
for _, arg := range allArgs {
	if arg[0] == '"' {
		arg = arg[1 : len(arg)-1]
	}
	fmt.Println(arg)
}

Output:

unimportant
-fb
quoted string