# arg-go

**Repository Path**: wick.zt/arg-go

## Basic Information

- **Project Name**: arg-go
- **Description**: Setup command line arguments by adding struct tag "arg".
- **Primary Language**: Go
- **License**: Not specified
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 1
- **Forks**: 0
- **Created**: 2022-03-18
- **Last Updated**: 2022-04-27

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# Arg, a struct config parser

[toc]

## Usage

This package is used for binding a struct (i.e., `Configure`) to the command line arguments.  So that the user can both load the config variables from file (yaml, json, toml, ...) and command line.

### Example

```go
package main

import (
    "gitee.com/wick.zt/arg-go"
)

type conf struct {
    Host     string `arg:"--host,<127.0.0.1>,:redis server host"`
    Port     uint16 `arg:"-p,--port,<6379>,:redis server port"`
    Password string `arg:"--password,:redis connection password"`
    Dryrun   bool   `arg:"-d,--dryrun,:do not act if set"`
    Negative bool   `arg:"-n,--negative,<true>,:test negative bool value"`
    Skip     int    // arg parser will skip this field
    Operate  string `arg:"-x,+r,:operation to act on server"`
}

func main() {
    c := &conf{}
    if err := arg.Prepare(c); err != nil {
        panic(err)
    }
    verbose := arg.NewFlag("Verbose", 'v', "verbose", "show debug messages", false)
    if err := arg.AddFlag(verbose, arg.OrderPreferred, func(interface{}) error {
        fmt.Println("set log level to debug")
    }); err != nil {
        panic(err)
    }
    if err := arg.Parse(); err != nil {
        panic(err)
    }
    fmt.Printf("Config: %+v\n", c) // ... use conf `c`
}

// $ main --password secret -x op
// Config: &{Host:127.0.0.1 Port:6379 Password:secret Dryrun:false Negative:true Skip:0 Operate:op}
```

### Example Usage

```txt
$ main --help
Usage of main:
    main [-h] [-d] [--host Host] -x Operate [--password Password] [-p Port]

Flags:
    -h,--help
        show this message and exit
    -v,--verbose
        show debug messages

Options:
    -d,--dryrun
        do not act if set
    --host HOST
        redis server host (default: 127.0.0.1)
    -n,--negative
        test negative bool value (default: true)
    -x OPERATE
        operation to act on server (required)
    --password PASSWORD
        redis connection password
    -p,--port PORT
        redis server port (default: 6379)

```

## Struct tag

Use struct tag `arg` and here're some tokens in the struct tag:

- `-a` Token starts with a single `-` and following with a single character is a short flag.
- `--foobar` Token starts with `--` and following with a word or phase is a long flag.
- `<value>` Token wrapped by `<` and `>` will be parsed as the default value, and will use the "zero value" of the field type if this is not specified.
- `+r` Token starts with a `+` and following with a single character is an attribute.
- `:usage` Token starts with a `:` and following with a sentence is the help message or description of the struct field.

The tokens is separated by `","` as the Golang libs usually do.

## Attributes

| Attr | Descption |
| ---- | --------- |
|    r |  required |
|    0 | no following arg (auto set for `bool` type) |
|    1 | 1 following arg (auto set for all other types) |
|    n | multiple following arg (not supported yet) |

## What todo next

- [X] ~~Parse `-h` and `--help` flag and show the usage~~
- [ ] Support multiple-arguments arg
- [ ] Support position dependent arg
- [X] ~~Support nested struct type~~
- [X] ~~Support `time.Duration` type~~