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// Copyright 2013 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package command allows you to define subcommands
// for your command line interfaces. It extends the flag package
// to provide flag support for subcommands.
package command
import (
"flag"
"fmt"
"os"
"sort"
"strings"
)
var (
OutFileDesc = os.Stdout
)
// A map of all of the registered sub-commands.
var cmds map[string]*cmdCont = make(map[string]*cmdCont)
// Matching subcommand.
var matchingCmd *cmdCont
// Arguments to call subcommand's runnable.
var args []string
// Flag to determine whether help is
// asked for subcommand or not
var flagHelp *bool
var definedHelp *Cmd = nil
// Cmd represents a sub command, allowing to define subcommand
// flags and runnable to run once arguments match the subcommand
// requirements.
type Cmd interface {
Flags(*flag.FlagSet) *flag.FlagSet
Run(args []string, definedFlags map[string]*flag.Flag)
}
type cmdCont struct {
name string
desc string
command Cmd
requiredFlags []string
definedFlags map[string]*flag.Flag
}
// Registers a Cmd for the provided sub-command name. E.g. name is the
// `status` in `git status`.
func On(name, description string, command Cmd, requiredFlags []string) {
cmds[name] = &cmdCont{
name: name,
desc: description,
command: command,
requiredFlags: requiredFlags,
}
}
func printUsageSorted(mapping map[string]*cmdCont) {
keys := []string{}
for key := range mapping {
keys = append(keys, key)
}
sort.Strings(keys)
for _, key := range keys {
cont := mapping[key]
fmt.Fprintf(OutFileDesc, " %-15s %s\n", key, cont.desc)
}
}
// Prints the usage.
func Usage() {
program := os.Args[0]
if len(cmds) == 0 {
// no subcommands
fmt.Fprintf(OutFileDesc, "Usage of %s:\n", program)
flag.PrintDefaults()
return
}
fmt.Fprintf(OutFileDesc, "Usage: %s <command>\n\n", program)
fmt.Fprintf(OutFileDesc, "where <command> is one of:\n")
printUsageSorted(cmds)
if numOfGlobalFlags() > 0 {
fmt.Fprintf(OutFileDesc, "\navailable flags:\n")
flag.PrintDefaults()
}
fmt.Fprintf(OutFileDesc, "\n%s <command> -h for subcommand help\n", program)
}
func subcommandUsage(cont *cmdCont) {
fmt.Fprintf(OutFileDesc, "Usage of %s %s:\n", os.Args[0], cont.name)
// should only output sub command flags, ignore h flag.
fs := matchingCmd.command.Flags(flag.NewFlagSet(cont.name, flag.ContinueOnError))
fs.PrintDefaults()
if len(cont.requiredFlags) > 0 {
fmt.Fprintf(OutFileDesc, "\nrequired flags:\n")
fmt.Fprintf(OutFileDesc, " %s\n\n", strings.Join(cont.requiredFlags, ", "))
}
}
// Parses the flags and leftover arguments to match them with a
// sub-command. Evaluate all of the global flags and register
// sub-command handlers before calling it. Sub-command handler's
// `Run` will be called if there is a match.
// A usage with flag defaults will be printed if provided arguments
// don't match the configuration.
// Global flags are accessible once Parse executes.
func Parse() {
helpCmd := definedHelp
canCallHelp := true
if helpCmd == nil {
canCallHelp = false
var helpCmdV *cmdCont
helpCmdV, canCallHelp = cmds["help"]
if canCallHelp && helpCmdV != nil {
helpCmd = &helpCmdV.command
}
}
if canCallHelp {
flag.Usage = func() {
(*helpCmd).Run(os.Args[2:], map[string]*flag.Flag{})
}
}
flag.Parse()
// if there are no subcommands registered,
// return immediately
if len(cmds) < 1 {
return
}
flag.Usage = Usage
if flag.NArg() < 1 {
flag.Usage()
os.Exit(1)
}
name := flag.Arg(0)
if cont, ok := cmds[name]; ok {
fs := cont.command.Flags(flag.NewFlagSet(name, flag.ExitOnError))
flagHelp = fs.Bool("h", false, "")
fs.Parse(flag.Args()[1:])
args = fs.Args()
matchingCmd = cont
// Check for required flags.
flagMap := make(map[string]bool)
for _, flagName := range cont.requiredFlags {
flagMap[flagName] = true
}
definedFlags := make(map[string]*flag.Flag)
fs.Visit(func(f *flag.Flag) {
definedFlags[f.Name] = f
delete(flagMap, f.Name)
})
cont.definedFlags = definedFlags
if len(flagMap) > 0 {
subcommandUsage(matchingCmd)
os.Exit(1)
}
} else {
flag.Usage()
os.Exit(1)
}
}
// Runs the subcommand's runnable. If there is no subcommand
// registered, it silently returns.
func Run() {
if matchingCmd != nil {
if *flagHelp {
subcommandUsage(matchingCmd)
return
}
matchingCmd.command.Run(args, matchingCmd.definedFlags)
}
}
// Parses flags and run's matching subcommand's runnable.
func ParseAndRun() {
Parse()
Run()
}
// Returns the total number of globally registered flags.
func numOfGlobalFlags() (count int) {
flag.VisitAll(func(flag *flag.Flag) {
count++
})
return
}
func DefineHelp(help Cmd) {
definedHelp = &help
}
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