Initial commit
diff --git a/CONTRIBUTING b/CONTRIBUTING
new file mode 100644
index 0000000..2827b7d
--- /dev/null
+++ b/CONTRIBUTING
@@ -0,0 +1,27 @@
+Want to contribute? Great! First, read this page (including the small print at the end).
+
+### Before you contribute
+Before we can use your code, you must sign the
+[Google Individual Contributor License Agreement]
+(https://cla.developers.google.com/about/google-individual)
+(CLA), which you can do online. The CLA is necessary mainly because you own the
+copyright to your changes, even after your contribution becomes part of our
+codebase, so we need your permission to use and distribute your code. We also
+need to be sure of various other things—for instance that you'll tell us if you
+know that your code infringes on other people's patents. You don't have to sign
+the CLA until after you've submitted your code for review and a member has
+approved it, but you must do it before we can put your code into our codebase.
+Before you start working on a larger contribution, you should get in touch with
+us first through the issue tracker with your idea so that we can help out and
+possibly guide you. Coordinating up front makes it much easier to avoid
+frustration later on.
+
+### Code reviews
+All submissions, including submissions by project members, require review. We
+use Github pull requests for this purpose.
+
+### The small print
+Contributions made by corporations are covered by a different agreement than
+the one above, the
+[Software Grant and Corporate Contributor License Agreement]
+(https://cla.developers.google.com/about/google-corporate).
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..d645695
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,202 @@
+
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+ http://www.apache.org/licenses/
+
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diff --git a/README.md b/README.md
new file mode 100644
index 0000000..c64665c
--- /dev/null
+++ b/README.md
@@ -0,0 +1,4 @@
+Subcommands is a Go package that implements a simple way for a single command to
+have many subcommands, each of which takes arguments and so forth.
+
+This is not an official Google product.
diff --git a/subcommands.go b/subcommands.go
new file mode 100644
index 0000000..4558947
--- /dev/null
+++ b/subcommands.go
@@ -0,0 +1,387 @@
+/*
+Copyright 2016 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 subcommands implements a simple way for a single command to have many
+// subcommands, each of which takes arguments and so forth.
+package subcommands
+
+import (
+ "fmt"
+ "io"
+ "os"
+ "path"
+ "sort"
+
+ "flag"
+"golang.org/x/net/context"
+)
+
+// A Command represents a single command.
+type Command interface {
+ // Name returns the name of the command.
+ Name() string
+
+ // Synopsis returns a short string (less than one line) describing the command.
+ Synopsis() string
+
+ // Usage returns a long string explaining the command and giving usage
+ // information.
+ Usage() string
+
+ // SetFlags adds the flags for this command to the specified set.
+ SetFlags(*flag.FlagSet)
+
+ // Execute executes the command and returns an ExitStatus.
+ Execute(ctx context.Context, f *flag.FlagSet, args ...interface{}) ExitStatus
+}
+
+// A Commander represents a set of commands.
+type Commander struct {
+ commands []*commandGroup
+ topFlags *flag.FlagSet // top-level flags
+ important []string // important top-level flags
+ name string // normally path.Base(os.Args[0])
+}
+
+// A commandGroup represents a set of commands about a common topic.
+type commandGroup struct {
+ name string
+ commands []Command
+}
+
+// An ExitStatus represents a Posix exit status that a subcommand
+// expects to be returned to the shell.
+type ExitStatus int
+
+const (
+ ExitSuccess ExitStatus = iota
+ ExitFailure
+ ExitUsageError
+)
+
+// NewCommander returns a new commander with the specified top-level
+// flags and command name. The Usage function for the topLevelFlags
+// will be set as well.
+func NewCommander(topLevelFlags *flag.FlagSet, name string) *Commander {
+ cdr := &Commander{
+ topFlags: topLevelFlags,
+ name: name,
+ }
+ topLevelFlags.Usage = func() { cdr.explain(os.Stderr) }
+ return cdr
+}
+
+// Register adds a subcommand to the supported subcommands in the
+// specified group. (Help output is sorted and arranged by group name.)
+// The empty string is an acceptable group name; such subcommands are
+// explained first before named groups.
+func (cdr *Commander) Register(cmd Command, group string) {
+ for _, g := range cdr.commands {
+ if g.name == group {
+ g.commands = append(g.commands, cmd)
+ return
+ }
+ }
+ cdr.commands = append(cdr.commands, &commandGroup{
+ name: group,
+ commands: []Command{cmd},
+ })
+}
+
+// ImportantFlag marks a top-level flag as important, which means it
+// will be printed out as part of the output of an ordinary "help"
+// subcommand. (All flags, important or not, are printed by the
+// "flags" subcommand.)
+func (cdr *Commander) ImportantFlag(name string) {
+ cdr.important = append(cdr.important, name)
+}
+
+// Execute should be called once the top-level-flags on a Commander
+// have been initialized. It finds the correct subcommand and executes
+// it, and returns an ExitStatus with the result. On a usage error, an
+// appropriate message is printed to os.Stderr, and ExitUsageError is
+// returned. The additional args are provided as-is to the Execute method
+// of the selected Command.
+func (cdr *Commander) Execute(ctx context.Context, args ...interface{}) ExitStatus {
+ if cdr.topFlags.NArg() < 1 {
+ cdr.topFlags.Usage()
+ return ExitUsageError
+ }
+
+ name := cdr.topFlags.Arg(0)
+
+ for _, group := range cdr.commands {
+ for _, cmd := range group.commands {
+ if name != cmd.Name() {
+ continue
+ }
+ f := flag.NewFlagSet(name, flag.ContinueOnError)
+ f.Usage = func() { explain(os.Stderr, cmd) }
+ cmd.SetFlags(f)
+ if f.Parse(cdr.topFlags.Args()[1:]) != nil {
+ return ExitUsageError
+ }
+ return cmd.Execute(ctx, f, args...)
+ }
+ }
+
+ // Cannot find this command.
+ cdr.topFlags.Usage()
+ return ExitUsageError
+}
+
+// Sorting of a slice of command groups.
+type byGroupName []*commandGroup
+
+func (p byGroupName) Len() int { return len(p) }
+func (p byGroupName) Less(i, j int) bool { return p[i].name < p[j].name }
+func (p byGroupName) Swap(i, j int) { p[i], p[j] = p[j], p[i] }
+
+// explain prints a brief description of all the subcommands and the
+// important top-level flags.
+func (cdr *Commander) explain(w io.Writer) {
+ fmt.Fprintf(w, "Usage: %s <flags> <subcommand> <subcommand args>\n\n", cdr.name)
+ sort.Sort(byGroupName(cdr.commands))
+ for _, group := range cdr.commands {
+ explainGroup(w, group)
+ }
+ if cdr.topFlags == nil {
+ fmt.Fprintln(w, "\nNo top level flags.")
+ return
+ }
+ if len(cdr.important) == 0 {
+ fmt.Fprintf(w, "\nUse \"%s flags\" for a list of top-level flags\n", cdr.name)
+ return
+ }
+
+ fmt.Fprintf(w, "\nTop-level flags (use \"%s flags\" for a full list):\n", cdr.name)
+ for _, name := range cdr.important {
+ f := cdr.topFlags.Lookup(name)
+ if f == nil {
+ panic("Important flag is not defined")
+ }
+ fmt.Fprintf(w, " -%s=%s: %s\n", f.Name, f.DefValue, f.Usage)
+ }
+}
+
+// Sorting of the commands within a group.
+func (g commandGroup) Len() int { return len(g.commands) }
+func (g commandGroup) Less(i, j int) bool { return g.commands[i].Name() < g.commands[j].Name() }
+func (g commandGroup) Swap(i, j int) { g.commands[i], g.commands[j] = g.commands[j], g.commands[i] }
+
+// explainGroup explains all the subcommands for a particular group.
+func explainGroup(w io.Writer, group *commandGroup) {
+ if len(group.commands) == 0 {
+ return
+ }
+ if group.name == "" {
+ fmt.Fprintf(w, "Subcommands:\n")
+ } else {
+ fmt.Fprintf(w, "Subcommands for %s:\n", group.name)
+ }
+ sort.Sort(group)
+ for _, cmd := range group.commands {
+ fmt.Fprintf(w, "\t%-15s %s\n", cmd.Name(), cmd.Synopsis())
+ }
+ fmt.Fprintln(w)
+}
+
+// explainCmd prints a brief description of a single command.
+func explain(w io.Writer, cmd Command) {
+ fmt.Fprintf(w, "%s", cmd.Usage())
+ subflags := flag.NewFlagSet(cmd.Name(), flag.PanicOnError)
+ subflags.SetOutput(w)
+ cmd.SetFlags(subflags)
+ subflags.PrintDefaults()
+}
+
+// A helper is a Command implementing a "help" command for
+// a given Commander.
+type helper Commander
+
+func (h *helper) Name() string { return "help" }
+func (h *helper) Synopsis() string { return "describe subcommands and their syntax" }
+func (h *helper) SetFlags(*flag.FlagSet) {}
+func (h *helper) Usage() string {
+ return `help [<subcommand>]:
+ With an argument, prints detailed information on the use of
+ the specified subcommand. With no argument, print a list of
+ all commands and a brief description of each.
+`
+}
+func (h *helper) Execute(_ context.Context, f *flag.FlagSet, args ...interface{}) ExitStatus {
+ switch f.NArg() {
+ case 0:
+ (*Commander)(h).explain(os.Stdout)
+ return ExitSuccess
+
+ case 1:
+ for _, group := range h.commands {
+ for _, cmd := range group.commands {
+ if f.Arg(0) != cmd.Name() {
+ continue
+ }
+ explain(os.Stdout, cmd)
+ return ExitSuccess
+ }
+ }
+ fmt.Fprintf(os.Stderr, "Subcommand %s not understood\n", f.Arg(0))
+ }
+
+ f.Usage()
+ return ExitUsageError
+}
+
+// HelpCommand returns a Command which implements a "help" subcommand.
+func (cdr *Commander) HelpCommand() Command {
+ return (*helper)(cdr)
+}
+
+// A flagger is a Command implementing a "flags" command for a given Commander.
+type flagger Commander
+
+func (flg *flagger) Name() string { return "flags" }
+func (flg *flagger) Synopsis() string { return "describe all known top-level flags" }
+func (flg *flagger) SetFlags(*flag.FlagSet) {}
+func (flg *flagger) Usage() string {
+ return `flags [<subcommand>]:
+ With an argument, print all flags of <subcommand>. Else,
+ print a description of all known top-level flags. (The basic
+ help information only discusses the most generally important
+ top-level flags.)
+`
+}
+func (flg *flagger) Execute(_ context.Context, f *flag.FlagSet, _ ...interface{}) ExitStatus {
+ if f.NArg() > 1 {
+ f.Usage()
+ return ExitUsageError
+ }
+
+ if f.NArg() == 0 {
+ if flg.topFlags == nil {
+ fmt.Println("No top-level flags are defined.")
+ } else {
+ flg.topFlags.PrintDefaults()
+ }
+ return ExitSuccess
+ }
+
+ for _, group := range flg.commands {
+ for _, cmd := range group.commands {
+ if f.Arg(0) != cmd.Name() {
+ continue
+ }
+ subflags := flag.NewFlagSet(cmd.Name(), flag.PanicOnError)
+ subflags.SetOutput(os.Stdout)
+ cmd.SetFlags(subflags)
+ subflags.PrintDefaults()
+ return ExitSuccess
+ }
+ }
+ fmt.Fprintf(os.Stderr, "Subcommand %s not understood\n", f.Arg(0))
+ return ExitFailure
+}
+
+// FlagsCommand returns a Command which implements a "flags" subcommand.
+func (cdr *Commander) FlagsCommand() Command {
+ return (*flagger)(cdr)
+}
+
+// A lister is a Command implementing a "commands" command for a given Commander.
+type lister Commander
+
+func (l *lister) Name() string { return "commands" }
+func (l *lister) Synopsis() string { return "list all command names" }
+func (l *lister) SetFlags(*flag.FlagSet) {}
+func (l *lister) Usage() string {
+ return `commands:
+ Print a list of all commands.
+`
+}
+func (l *lister) Execute(_ context.Context, f *flag.FlagSet, _ ...interface{}) ExitStatus {
+ if f.NArg() != 0 {
+ f.Usage()
+ return ExitUsageError
+ }
+
+ for _, group := range l.commands {
+ for _, cmd := range group.commands {
+ fmt.Printf("%s\n", cmd.Name())
+ }
+ }
+ return ExitSuccess
+}
+
+// CommandsCommand returns Command which implements a "commands" subcommand.
+func (cdr *Commander) CommandsCommand() Command {
+ return (*lister)(cdr)
+}
+
+// DefaultCommander is the default commander using flag.CommandLine for flags
+// and os.Args[0] for the command name.
+var DefaultCommander *Commander
+
+func init() {
+ DefaultCommander = NewCommander(flag.CommandLine, path.Base(os.Args[0]))
+}
+
+// Register adds a subcommand to the supported subcommands in the
+// specified group. (Help output is sorted and arranged by group
+// name.) The empty string is an acceptable group name; such
+// subcommands are explained first before named groups. It is a
+// wrapper around DefaultCommander.Register.
+func Register(cmd Command, group string) {
+ DefaultCommander.Register(cmd, group)
+}
+
+// ImportantFlag marks a top-level flag as important, which means it
+// will be printed out as part of the output of an ordinary "help"
+// subcommand. (All flags, important or not, are printed by the
+// "flags" subcommand.) It is a wrapper around
+// DefaultCommander.ImportantFlag.
+func ImportantFlag(name string) {
+ DefaultCommander.ImportantFlag(name)
+}
+
+// Execute should be called once the default flags have been
+// initialized by flag.Parse. It finds the correct subcommand and
+// executes it, and returns an ExitStatus with the result. On a usage
+// error, an appropriate message is printed to os.Stderr, and
+// ExitUsageError is returned. The additional args are provided as-is
+// to the Execute method of the selected Command. It is a wrapper
+// around DefaultCommander.Execute.
+func Execute(ctx context.Context, args ...interface{}) ExitStatus {
+ return DefaultCommander.Execute(ctx, args...)
+}
+
+// HelpCommand returns a Command which implements "help" for the
+// DefaultCommander. Use Register(HelpCommand(), <group>) for it to be
+// recognized.
+func HelpCommand() Command {
+ return DefaultCommander.HelpCommand()
+}
+
+// FlagsCommand returns a Command which implements "flags" for the
+// DefaultCommander. Use Register(FlagsCommand(), <group>) for it to be
+// recognized.
+func FlagsCommand() Command {
+ return DefaultCommander.FlagsCommand()
+}
+
+// CommandsCommand returns Command which implements a "commands" subcommand.
+func CommandsCommand() Command {
+ return DefaultCommander.CommandsCommand()
+}
