mirror of
https://github.com/thegeeklab/github-releases-notifier.git
synced 2024-09-21 16:42:46 +02:00
322 lines
6.5 KiB
Markdown
322 lines
6.5 KiB
Markdown
[](https://godoc.org/github.com/alexflint/go-arg)
|
|
[](https://travis-ci.org/alexflint/go-arg)
|
|
[](https://coveralls.io/github/alexflint/go-arg?branch=master)
|
|
[](https://goreportcard.com/badge/github.com/alexflint/go-arg)
|
|
|
|
## Structured argument parsing for Go
|
|
|
|
```shell
|
|
go get github.com/alexflint/go-arg
|
|
```
|
|
|
|
Declare the command line arguments your program accepts by defining a struct.
|
|
|
|
```go
|
|
var args struct {
|
|
Foo string
|
|
Bar bool
|
|
}
|
|
arg.MustParse(&args)
|
|
fmt.Println(args.Foo, args.Bar)
|
|
```
|
|
|
|
```shell
|
|
$ ./example --foo=hello --bar
|
|
hello true
|
|
```
|
|
|
|
### Required arguments
|
|
|
|
```go
|
|
var args struct {
|
|
ID int `arg:"required"`
|
|
Timeout time.Duration
|
|
}
|
|
arg.MustParse(&args)
|
|
```
|
|
|
|
```shell
|
|
$ ./example
|
|
Usage: example --id ID [--timeout TIMEOUT]
|
|
error: --id is required
|
|
```
|
|
|
|
### Positional arguments
|
|
|
|
```go
|
|
var args struct {
|
|
Input string `arg:"positional"`
|
|
Output []string `arg:"positional"`
|
|
}
|
|
arg.MustParse(&args)
|
|
fmt.Println("Input:", args.Input)
|
|
fmt.Println("Output:", args.Output)
|
|
```
|
|
|
|
```
|
|
$ ./example src.txt x.out y.out z.out
|
|
Input: src.txt
|
|
Output: [x.out y.out z.out]
|
|
```
|
|
|
|
### Environment variables
|
|
|
|
```go
|
|
var args struct {
|
|
Workers int `arg:"env"`
|
|
}
|
|
arg.MustParse(&args)
|
|
fmt.Println("Workers:", args.Workers)
|
|
```
|
|
|
|
```
|
|
$ WORKERS=4 ./example
|
|
Workers: 4
|
|
```
|
|
|
|
```
|
|
$ WORKERS=4 ./example --workers=6
|
|
Workers: 6
|
|
```
|
|
|
|
You can also override the name of the environment variable:
|
|
|
|
```go
|
|
var args struct {
|
|
Workers int `arg:"env:NUM_WORKERS"`
|
|
}
|
|
arg.MustParse(&args)
|
|
fmt.Println("Workers:", args.Workers)
|
|
```
|
|
|
|
```
|
|
$ NUM_WORKERS=4 ./example
|
|
Workers: 4
|
|
```
|
|
|
|
### Usage strings
|
|
```go
|
|
var args struct {
|
|
Input string `arg:"positional"`
|
|
Output []string `arg:"positional"`
|
|
Verbose bool `arg:"-v,help:verbosity level"`
|
|
Dataset string `arg:"help:dataset to use"`
|
|
Optimize int `arg:"-O,help:optimization level"`
|
|
}
|
|
arg.MustParse(&args)
|
|
```
|
|
|
|
```shell
|
|
$ ./example -h
|
|
Usage: [--verbose] [--dataset DATASET] [--optimize OPTIMIZE] [--help] INPUT [OUTPUT [OUTPUT ...]]
|
|
|
|
Positional arguments:
|
|
INPUT
|
|
OUTPUT
|
|
|
|
Options:
|
|
--verbose, -v verbosity level
|
|
--dataset DATASET dataset to use
|
|
--optimize OPTIMIZE, -O OPTIMIZE
|
|
optimization level
|
|
--help, -h print this help message
|
|
```
|
|
|
|
### Default values
|
|
|
|
```go
|
|
var args struct {
|
|
Foo string
|
|
Bar bool
|
|
}
|
|
args.Foo = "default value"
|
|
arg.MustParse(&args)
|
|
```
|
|
|
|
### Arguments with multiple values
|
|
```go
|
|
var args struct {
|
|
Database string
|
|
IDs []int64
|
|
}
|
|
arg.MustParse(&args)
|
|
fmt.Printf("Fetching the following IDs from %s: %q", args.Database, args.IDs)
|
|
```
|
|
|
|
```shell
|
|
./example -database foo -ids 1 2 3
|
|
Fetching the following IDs from foo: [1 2 3]
|
|
```
|
|
|
|
### Arguments that can be specified multiple times, mixed with positionals
|
|
```go
|
|
var args struct {
|
|
Commands []string `arg:"-c,separate"`
|
|
Files []string `arg:"-f,separate"`
|
|
Databases []string `arg:"positional"`
|
|
}
|
|
```
|
|
|
|
```shell
|
|
./example -c cmd1 db1 -f file1 db2 -c cmd2 -f file2 -f file3 db3 -c cmd3
|
|
Commands: [cmd1 cmd2 cmd3]
|
|
Files [file1 file2 file3]
|
|
Databases [db1 db2 db3]
|
|
```
|
|
|
|
### Custom validation
|
|
```go
|
|
var args struct {
|
|
Foo string
|
|
Bar string
|
|
}
|
|
p := arg.MustParse(&args)
|
|
if args.Foo == "" && args.Bar == "" {
|
|
p.Fail("you must provide one of --foo and --bar")
|
|
}
|
|
```
|
|
|
|
```shell
|
|
./example
|
|
Usage: samples [--foo FOO] [--bar BAR]
|
|
error: you must provide one of --foo and --bar
|
|
```
|
|
|
|
### Version strings
|
|
|
|
```go
|
|
type args struct {
|
|
...
|
|
}
|
|
|
|
func (args) Version() string {
|
|
return "someprogram 4.3.0"
|
|
}
|
|
|
|
func main() {
|
|
var args args
|
|
arg.MustParse(&args)
|
|
}
|
|
```
|
|
|
|
```shell
|
|
$ ./example --version
|
|
someprogram 4.3.0
|
|
```
|
|
|
|
### Embedded structs
|
|
|
|
The fields of embedded structs are treated just like regular fields:
|
|
|
|
```go
|
|
|
|
type DatabaseOptions struct {
|
|
Host string
|
|
Username string
|
|
Password string
|
|
}
|
|
|
|
type LogOptions struct {
|
|
LogFile string
|
|
Verbose bool
|
|
}
|
|
|
|
func main() {
|
|
var args struct {
|
|
DatabaseOptions
|
|
LogOptions
|
|
}
|
|
arg.MustParse(&args)
|
|
}
|
|
```
|
|
|
|
As usual, any field tagged with `arg:"-"` is ignored.
|
|
|
|
### Custom parsing
|
|
|
|
You can implement your own argument parser by implementing `encoding.TextUnmarshaler`:
|
|
|
|
```go
|
|
package main
|
|
|
|
import (
|
|
"fmt"
|
|
"strings"
|
|
|
|
"github.com/alexflint/go-arg"
|
|
)
|
|
|
|
// Accepts command line arguments of the form "head.tail"
|
|
type NameDotName struct {
|
|
Head, Tail string
|
|
}
|
|
|
|
func (n *NameDotName) UnmarshalText(b []byte) error {
|
|
s := string(b)
|
|
pos := strings.Index(s, ".")
|
|
if pos == -1 {
|
|
return fmt.Errorf("missing period in %s", s)
|
|
}
|
|
n.Head = s[:pos]
|
|
n.Tail = s[pos+1:]
|
|
return nil
|
|
}
|
|
|
|
func main() {
|
|
var args struct {
|
|
Name *NameDotName
|
|
}
|
|
arg.MustParse(&args)
|
|
fmt.Printf("%#v\n", args.Name)
|
|
}
|
|
```
|
|
```shell
|
|
$ ./example --name=foo.bar
|
|
&main.NameDotName{Head:"foo", Tail:"bar"}
|
|
|
|
$ ./example --name=oops
|
|
Usage: example [--name NAME]
|
|
error: error processing --name: missing period in "oops"
|
|
```
|
|
|
|
### Description strings
|
|
|
|
```go
|
|
type args struct {
|
|
Foo string
|
|
}
|
|
|
|
func (args) Description() string {
|
|
return "this program does this and that"
|
|
}
|
|
|
|
func main() {
|
|
var args args
|
|
arg.MustParse(&args)
|
|
}
|
|
```
|
|
|
|
```shell
|
|
$ ./example -h
|
|
this program does this and that
|
|
Usage: example [--foo FOO]
|
|
|
|
Options:
|
|
--foo FOO
|
|
--help, -h display this help and exit
|
|
```
|
|
|
|
### Documentation
|
|
|
|
https://godoc.org/github.com/alexflint/go-arg
|
|
|
|
### Rationale
|
|
|
|
There are many command line argument parsing libraries for Go, including one in the standard library, so why build another?
|
|
|
|
The shortcomings of the `flag` library that ships in the standard library are well known. Positional arguments must preceed options, so `./prog x --foo=1` does what you expect but `./prog --foo=1 x` does not. Arguments cannot have both long (`--foo`) and short (`-f`) forms.
|
|
|
|
Many third-party argument parsing libraries are geared for writing sophisticated command line interfaces. The excellent `codegangsta/cli` is perfect for working with multiple sub-commands and nested flags, but is probably overkill for a simple script with a handful of flags.
|
|
|
|
The main idea behind `go-arg` is that Go already has an excellent way to describe data structures using Go structs, so there is no need to develop more levels of abstraction on top of this. Instead of one API to specify which arguments your program accepts, and then another API to get the values of those arguments, why not replace both with a single struct?
|