flag

The flag driver reads values from command line flags.

import "github.com/insei/tinyconf/drivers/flag"

flagDriver, err := flag.New()

Add it last, so the flags have the highest priority:

config, err := tinyconf.New(
    tinyconf.WithDriver(tagDriver),
    tinyconf.WithDriver(yamlDriver),
    tinyconf.WithDriver(envDriver),
    tinyconf.WithDriver(flagDriver),
)

Names

The flag tag is the name of the flag without dashes:

type Config struct {
    HTTP struct {
        Host string `flag:"http-host" doc:"http host"`
        Port int    `flag:"http-port" doc:"http port"`
    }
    Hosts   []string `flag:"host" doc:"allowed hosts"`
    Verbose bool     `flag:"verbose"`
}

app --http-host=example.com --http-port 9090 --host=a --host=b -verbose

A field without the flag tag is not read from the command line.

Supported forms

Form	Example
-name=value, --name=value	--http-port=9090
-name value, --name value	--http-port 9090
-name, --name for bool fields	--verbose

• Bool fields do not take the next argument as a value: use --verbose=false to set false.
• Slices and arrays can be filled with repeated flags: --host=a --host=b,c is [a b c]. For all other types the last occurrence of the flag is used.
• All arguments after -- are ignored.
• Values are parsed by the rules of string values.

Unknown flags

The driver does not own the command line: it only looks for the flags of the config fields. Unknown flags and positional arguments are ignored, so the driver can be used together with the flag package of the standard library or with any CLI framework.

No --help

The driver does not handle -h and --help. Print GenDoc("flag") from your own handler of the help flag.

Custom arguments

By default os.Args[1:] is used. Custom arguments are set with WithArgs, in tests or for sub commands:

flagDriver, err := flag.New(flag.WithArgs(os.Args[2:]))

Documentation

GenDoc("flag") generates the usage of all flags with descriptions from the doc tags and current values as defaults:

  -http-host
        http host (default example.com)
  -http-port
        http port (default 9090)
  -host
        allowed hosts (default a,b)
  -verbose
         (default false)

Values of the fields with hidden:"true" are not shown.