flag

Overview ¶

Package flag provides a simple API for defining and parsing command-line flags in Go applications.

It is built on top of the pflag library and includes support for a set of common default flags.

Default flags:

• `--path` (string): Sets the application’s default path (default: "./data")
• `--help` (bool): Displays the help message
• `--version` (bool): Prints the application version
• `--debug` (bool): Enables debug mode

The `Init` function parses all registered flags and should be called early, typically in the `main` function of the application. If the `--help` flag is set, it prints usage information and exits.

Additional flags can be registered using `Register`, which accepts the flag name, a pointer to the variable to populate, and a usage description. Existing flags can be overridden using `Override`, which allows changing the variable, default value, and description of an already registered flag. Flags can be removed using `Unregister`, which removes a previously registered flag from the command line. Supported types include strings, booleans, integers, unsigned integers, and floats.

Example:

package main

import (
	"fmt"
	"github.com/valentin-kaiser/go-core/flag"
)

var CustomFlag string

func main() {
	flag.Register("custom", &CustomFlag, "A custom flag for demonstration")

	// Override the default path flag
	flag.Path = "/new/default/path"
	flag.Override("path", &flag.Path, "Updated application working directory")

	// Unregister a flag if no longer needed
	flag.Unregister("custom")

	flag.Init()

	fmt.Println("Custom Flag Value:", CustomFlag)
	fmt.Println("Path:", flag.Path)
}