Parse strings like command line arguments with Go

Question

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)
}

pythonian 23 · Accepted Answer · 2022-04-06 17:49:52Z

4

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)

edited Apr 6, 2022 at 17:49

pythonian 23

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answered Feb 4, 2022 at 19:41

Nicholas Carey

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3 Comments

erdnaxeli Over a year ago

flag and pflag can both parse an arbitrary argv, see flag.FlagSet.Parse and pflag.FlagSet.Parse.

Nicholas Carey Over a year ago

@erdnaxeli — the original question is wanting to take an arbitrary string (as if entered on the command line) and parse it into "words" as the shell would do, producing an argv. For instance, the string foo bar"baz" -o some \file.name".txt" would be parsed into the words foo, barbaz, -o, and some file.name.txt. Then you need to decide whether or not you want to expand globs (you probably do).

erdnaxeli Over a year ago

Yes, you are right, my comment is off-topic.

Amirreza Noori · Accepted Answer · 2022-02-04 08:46:08Z

1

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

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

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

Information about regexp syntax: https://pkg.go.dev/regexp/[email protected]

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

edited Feb 4, 2022 at 8:46

answered Feb 4, 2022 at 5:31

Amirreza Noori

1,5251 gold badge8 silver badges24 bronze badges

2 Comments

pythonian 23 Over a year ago

What about escaped quotes like in unimportant -fb "quoted string \"with\" escaped quotes"?

Amirreza Noori Over a year ago

Regex changed in the answer: ([-a-zA-Z]+)|(".*?[^\\]")|("")

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