Add in-tool documentation

3 files changed, 60 insertions, 10 deletions

diff --git a/dec.go b/dec.go
index e67f4b3..d1404b7 100644
--- a/dec.go
+++ b/dec.go
@@ -22,6 +22,23 @@ type decryptFlags struct {
 func (f *decryptFlags) registerFlags(fs *flag.FlagSet) {
 	fs.StringVar(&f.password, "p", "", "use the specified password; if not provided, dec will prompt for a password")
 	fs.BoolVar(&f.force, "f", false, "overwrite output files even if they already exist")
+	fs.Usage = func() {
+		fmt.Fprintf(fs.Output(), `usage: %s [OPTION]... [FILE]...
+Decrypt files, or stdin if no files are provided.
+
+`,
+			fs.Name())
+		fs.PrintDefaults()
+		fmt.Fprintf(fs.Output(), `-p is required when reading from stdin.
+
+For example,
+  %s my-encrypted-file.txt.enc
+would decrypt my-encrypted-file.txt.enc and write the result to
+my-encrypted-file.txt. If a filename does not end with .enc, the name
+will be appended with a .dec extension.
+`,
+			fs.Name())
+	}
 }
 
 type decryptOptions struct {
diff --git a/enc.go b/enc.go
index 1217606..fc54756 100644
--- a/enc.go
+++ b/enc.go
@@ -23,6 +23,21 @@ func (f *encryptFlags) registerFlags(fs *flag.FlagSet) {
 	fs.BoolVar(&f.generatePassword, "g", false, "generate a secure password automatically (password will be printed to stderr)")
 	fs.StringVar(&f.password, "p", "", "use the specified password; if not provided, enc will prompt for a password")
 	fs.BoolVar(&f.force, "f", false, "overwrite output files even if they already exist")
+	fs.Usage = func() {
+		fmt.Fprintf(fs.Output(), `usage: %s [OPTION]... [FILE]...
+Encrypt files, or stdin if no files are provided.
+
+`,
+			fs.Name())
+		fs.PrintDefaults()
+		fmt.Fprintf(fs.Output(), `
+One of -g or -p must be used when reading from stdin. When encrypting to
+stdout, consider redirecting the result since binary output can mess up
+your terminal. Example:
+  echo test | %s -p 'my super secure password' | base64
+`,
+			fs.Name())
+	}
 }
 
 type encryptOptions struct {
diff --git a/sym.go b/sym.go
index e9eef94..c83ecbc 100644
--- a/sym.go
+++ b/sym.go
@@ -13,7 +13,7 @@ type subcommand interface {
 }
 
 func whichSubcommand(name string) (subcommand, bool) {
-	switch filepath.Base(name) {
+	switch name {
 	case "enc":
 		return &encryptOptions{
 			passwordIn:  termReadPassword,
@@ -33,20 +33,38 @@ func whichSubcommand(name string) (subcommand, bool) {
 }
 
 func run(args []string) error {
-	cmd, ok := whichSubcommand(args[0])
+	name := filepath.Base(args[0])
+	cmd, ok := whichSubcommand(name)
 	if !ok {
-		if len(args) < 2 {
-			return fmt.Errorf("missing subcommand")
+		flag.Usage = func() {
+			fmt.Fprintf(os.Stderr, `usage: sym <subcommand> [OPTION]... [FILE]...
+Encrypt or decrypt files using a password.
+
+Subcommands:
+  enc    encrypt
+  dec    decrypt
+
+Try sym <subcommand> -h for command-specific help.
+
+Pro tip: use "ln sym enc" or "ln sym dec" to create shortcuts for each subcommand.
+`)
+		}
+		flag.CommandLine.Parse(args[1:])
+		args = flag.Args()
+		if len(args) == 0 {
+			return fmt.Errorf("missing subcommand (use sym -h for help)")
 		}
-		cmd, ok = whichSubcommand(args[1])
+		subcommand := filepath.Base(args[0])
+		name = "sym " + subcommand
+		cmd, ok = whichSubcommand(subcommand)
 		if !ok {
-			return fmt.Errorf("invalid subcommand %q", args[1])
+			return fmt.Errorf("invalid subcommand %q", args[0])
 		}
-		args = args[1:]
 	}
-	cmd.registerFlags(flag.CommandLine)
-	flag.CommandLine.Parse(args[1:])
-	return cmd.run(flag.Args()...)
+	fs := flag.NewFlagSet(name, flag.ExitOnError)
+	cmd.registerFlags(fs)
+	fs.Parse(args[1:])
+	return cmd.run(fs.Args()...)
 }
 
 func main() {