README
¶
act
Microservices oriented 12-factor Go library for parsing environment variables and command line flags to arbitrary config struct using struct tags to define default values and to override flag names and environment variables' names.
This package in intended to be used to parse command line arguments and environment variables into an arbitrary config struct. This struct may contain multiple nested structs, they all will be processed recursively. Names of the flags and environment variables are automatically generated. Flags will be kebab case of the field name eventually preceded by parent fields in case of nested structs. Names of environment variables will be similar, but additionally prefixed with command name and then snake and upper cased. Description of each flag will also be automatically generated in a human friendly way as much as possible. Additionally, you may override these auto-generated names using the struct tags and you also may define default value.
- flag - override generated flag name
- env - override generated environment variable name
- help - override generated flag description
- def - override default (zero) value
Important: all struct fields should be exported.
Custom flag types
Besides the types supported by flag package, this package provides additional types:
- act.StringSlice - doesn't support multiple flags but instead supports comma separated strings, i.e. "foo,bar"
- act.IntSlice - doesn't support multiple flags but instead supports comma separated integers, i.e. "5,-8,0"
- act.URL
Order of precedence:
- command line options
- environment variables
- default values
Examples
Run make test-verbose to see examples output.
Subcommands
These are handled just like by standard library's flag package.
package main
import (
"log"
"os"
"go.ectobit.com/act"
)
func main() {
subCmd := os.Args[1]
switch subCmd {
case "create":
config := &struct{}{}
createCmd := act.New("create")
if err := createCmd.Parse(config, os.Args[2:]); err != nil {
log.Println(err)
}
// Implementation
case "delete":
config := &struct{}{}
deleteCmd := act.New("create")
if err := deleteCmd.Parse(config, os.Args[2:]); err != nil {
log.Println(err)
}
// Implementation
}
}
TODO
- support req struct tag to mark required values
Documentation
¶
Overview ¶
Package act is a library for parsing command line flags, environment variables and default values defined by struct tag "def" respecting the order of precedence according to the 12-factor principles. It generates predefined flag names and environment variables names by the fields path of the supplied config, but allows this to be overridden by struct tags "flag" and "env".
Example (Advanced) ¶
package main
import (
"flag"
"log"
"time"
"go.ectobit.com/act"
)
func main() {
type config struct {
Env string `help:"environment [development|production]" def:"development"`
Port uint `def:"3000"`
Mongo struct {
Hosts act.StringSlice `def:"mongo"`
ConnectionTimeout time.Duration `def:"10s"`
ReplicaSet string
MaxPoolSize uint64 `def:"100"`
TLS bool
Username string
Password string
Database string `def:"cool"`
}
JWT struct {
Secret string
TokenExpiration time.Duration `def:"24h"`
RefreshTokenExpiration time.Duration `def:"168h"`
}
AWS struct {
Region string `def:"eu-central-1"`
}
}
cfg := &config{} //nolint:exhaustivestruct
cmd := act.New("cool", act.WithErrorHandling(flag.ContinueOnError))
if err := cmd.Parse(cfg, []string{"-h"}); err != nil {
log.Println(err)
}
}
Output:
Example (Basic) ¶
package main
import (
"flag"
"log"
"go.ectobit.com/act"
)
func main() {
type config struct {
Host string
Port int
DB struct {
Kind string
Postgres struct {
Host string
}
Mongo struct {
Host act.StringSlice
}
}
}
cfg := &config{} //nolint:exhaustivestruct
cmd := act.New("mycmd", act.WithErrorHandling(flag.ContinueOnError))
if err := cmd.Parse(cfg, []string{"-h"}); err != nil {
log.Println(err)
}
}
Output:
Index ¶
Examples ¶
Constants ¶
This section is empty.
Variables ¶
var ( ErrInvalidConfigType = errors.New("invalid config type") ErrUnsupportedType = errors.New("type not supported") )
Errors.
Functions ¶
This section is empty.
Types ¶
type Act ¶
type Act struct {
// contains filtered or unexported fields
}
Act is an abstraction of a CLI command.
type IntSlice ¶
type IntSlice []int
IntSlice implements flag.Getter interface for []int type.
type Option ¶
type Option func(a *Act)
Option defines optional parameters to the constructor.
func WithErrorHandling ¶
func WithErrorHandling(errorHandling flag.ErrorHandling) Option
WithErrorHandling is an option to change error handling similar to flag package.
func WithLookupEnvFunc ¶
WithLookupEnvFunc may be used to override default os.LookupEnv function to read environment variables values.
func WithOutput ¶
WithOutput is an option to change the output writer similar as flag.SetOutput does.
type StringSlice ¶
type StringSlice []string
StringSlice implements flag.Getter interface for []string type.
func (*StringSlice) Set ¶
func (f *StringSlice) Set(s string) error
Set sets flag's value by splitting provided comma separated string.
Source Files