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// Handler to make management of subcommands easier.
package main
import (
"fmt"
"flag"
"os"
)
type (
Command struct {
Use string // command name (used for matching)
Short string // a short description to display
Long string // a long help text
Example string // an example string
Run func(*Command, []string) // the command to run
flagSet *flag.FlagSet // internal flagset with all flags
commands []*Command // the list of subcommands
}
)
// This function adds a new sub command.
func (c *Command) AddCommand(cmds... *Command) {
res := c.commands
for _, cmd := range cmds {
res = append(res, cmd)
}
c.commands = res
}
// Evaluate the arguments and call either the subcommand or parse it as flags.
func (c *Command) eval(args []string) error {
var name string = ""
var rest []string = []string{}
if len(args) > 0 {
name = args[0]
}
if len(args) > 1 {
rest = args[1:]
}
if name == "help" {
c.Help(rest)
return nil
}
for _, cmd := range c.commands {
if cmd.Use == name {
return cmd.eval(rest)
}
}
if err := c.Flags().Parse(rest); err != nil { return err }
if c.Run != nil {
c.Run(c, rest)
} else {
c.Help(rest)
}
return nil
}
// Execute the command. It will fetch os.Args[1:] itself.
func (c *Command) Execute() error {
return c.eval(os.Args[1:])
}
// Return the flagset currently in use.
func (c *Command) Flags() *flag.FlagSet {
if c.flagSet == nil {
c.flagSet = flag.NewFlagSet(c.Use, flag.ContinueOnError)
}
return c.flagSet
}
// Print the help for the current command or a subcommand.
func (c *Command) Help(args []string) {
if len(args) > 0 {
for _, cmd := range c.commands {
if args[0] == cmd.Use {
cmd.Help([]string{})
return
}
}
}
if c.Long != "" { fmt.Println(c.Long, "\n") }
c.Usage()
}
// Print the usage information.
func (c *Command) Usage() {
usage := ""
if c.Use != "" {
usage = usage + " " + c.Use
}
if len(c.commands) > 0 {
usage = usage + " command"
}
if c.flagSet != nil {
usage = usage + " [flags]"
}
fmt.Printf("Usage: %s%s\n", os.Args[0], usage)
if len(c.commands) > 0 {
fmt.Printf("\nwhere command is one of:\n")
for _, cmd := range c.commands {
fmt.Printf("\t%s\t\t%s\n", cmd.Use, cmd.Short)
}
}
if c.flagSet != nil {
fmt.Printf("\nwhere flags is any of:\n")
c.Flags().SetOutput(os.Stdout)
c.Flags().PrintDefaults()
}
if c.Example != "" {
fmt.Println("\nexample:")
fmt.Printf("\t%s\n", c.Example)
}
}
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