scli

Build a command line argument parser by defining a struct

Example

This example is in example/simple/main.go

// define flag, default and usage in struct field's tags
type Arg struct {
    // Flags(no value) are defined by bool type field
    Help bool `flag:"h" default:"false" usage:"print help"`

    // Arguments(with value) are defined by field of their types
    // define flag, default and usage in struct field's tags
    // flag, default and usage in tag are all optional
    Name  string `flag:"name" default:"you" usage:"your name"`
    Email string `flag:"email" default:"[email protected]" usage:"your email"`

    // subcommands are defined by *struct{...} field
    Add *struct {
        All  bool   `flag:"a" default:"false" usage:"Add all files"`
        File string `flag:"f" usage:"file to be added"`
    } `flag:"add" usage:"Add file contents to the index"`

    Commit *struct{} `flag:"commit" usage:"Record changes to the repository"`

    // subcommands can be nested inside of subcommands!
    Push *struct {
        Origin *struct{} `flag:"origin" usage:"Push to origin"`
    } `flag:"push" usage:"Push to remote repository"`
}

func main() {
    var arg Arg // init a empty argument struct

    parser := scli.BuildParser(&arg)
    parser.Parse()
    fmt.Printf("%v\n", prettyPrint(arg))
}

Below are some examples of input CLI arguments and parsed values of arg.

$ ./mygit
{
  "Help": false,
  "Name": "you",
  "Email": "[email protected]",
  "Add": null,
  "Commit": null,
  "Push": null
}

$ ./mygit --name canoriz
{
  "Help": false,
  "Name": "canoriz",
  "Email": "[email protected]",
  "Add": null,
  "Commit": null,
  "Push": null
}

$ ./mygit --name canoriz add -a -f source-code
{
  "Help": false,
  "Name": "canoriz",
  "Email": "[email protected]",
  "Add": {
    "All": true,
    "File": "source-code"
  },
  "Commit": null,
  "Push": null
}

$ ./mygit --name canoriz commit
{
  "Help": false,
  "Name": "canoriz",
  "Email": "[email protected]",
  "Add": null,
  "Commit": {},
  "Push": null
}

$ ./mygit --name canoriz push origin
{
  "Help": false,
  "Name": "canoriz",
  "Email": "[email protected]",
  "Add": null,
  "Commit": null,
  "Push": {
    "Origin": {}
  }
}

$ ./mygit --name canoriz push
{
  "Help": false,
  "Name": "canoriz",
  "Email": "[email protected]",
  "Add": null,
  "Commit": null,
  "Push": {
    "Origin": null
  }
}

$ ./mygit --name canoriz add
error: argument "--f" is required in "./mygit add" but not provided

The usage is:
Usage: ./mygit add [OPTIONS]

Options:
    -help, --help           print this message
    --a, --/a               set [Add all files] to true / false  [default: false]
    --f <file to be added>

$ ./mygit --help
Usage: ./mygit [OPTIONS] [COMMAND]

Commands:
    add     Add file contents to the index
    commit  Record changes to the repository
    push    Push to remote repository

Options:
    -help, --help         print this message
    --email <your email>  [default: "[email protected]"]
    --h, --/h             set [print help] to true / false  [default: false]
    --name <your name>    [default: "you"]

Run `./mygit [COMMAND] -help` to print the help message of COMMAND

$ ./mygit add --help
Usage: ./mygit add [OPTIONS]

Options:
    -help, --help           print this message
    --a, --/a               set [Add all files] to true / false  [default: false]
    --f <file to be added>

Feature

Any type of argument

Supports arguments of type int, float64, bool, string, []int, []float, []bool, []string, or any type T that *T implemented scli.Parse.

For example, if Addr {string; string} struct defines a (*Addr).FromString(string) error method parsing 127.0.0.1:80 to Addr {"127.0.0.1", "80"}, and a (*Addr).Example() string returns "1.2.3.4:5678", method.CLI can have a type Addr argument.

• ./my-program -addr 127.0.0.1:80

Arbitrary nested layer of subcommands

Supports defining CLI program like below, where remote, local are layer 1 subcommands, add, remove are layer 2 subcommands.

• ./my-program remote add -name Alice
• ./my-program local add -name Bob
• ./my-program remote remove -name Cindy

Any argument/subcommand can have a configurable CLI argument name and usage message.

Default values

Supports default value for any type of arguments by simply add a default tag, including custom types.

• type Arg struct {
      addr Addr `default:"127.0.0.1:80"`
  }
  

Notes for panic

To parse arguments, there are 2 stages.

1. BuildParser(*struct{...}) error) to build a parser
2. Parse(), ParseArgs(...)to parse arguments

BuildParser will check struct field's type and tags, if error found in type and tags, BuildParser panics and tells the detailed error. You can think BuildParser compile struct{...} to corresponding Parser, and compile may error.

Parse(), ParseArgs(...) parse input arguments from CLI or []string, they never panics, if parse fails, error is returned.

Parse() do a bit more than ParseArgs(...). If error occurred in Parse(), show parse errors and program USAGE, then program exits.

If a custom type Custom is in arguments struct, and the custom type's Custom.FromString(string) method may panic. If FromString panic, Parse() and ParseArg() will panic.