From 652c755d3751109d878a9c8228c0bcb7aed0d4f5 Mon Sep 17 00:00:00 2001
From: Unai Martinez-Corral <38422348+umarcor@users.noreply.github.com>
Date: Mon, 8 Feb 2021 00:08:50 +0000
Subject: [PATCH] Use golangci-lint (#1044)

Use golangci-lint. Repair warnings and errors resulting from linting.
---
 .golangci.yml                     |  48 +++++++
 .travis.yml                       |   9 +-
 Makefile                          |  18 +--
 README.md                         |   9 +-
 bash_completions.go               | 133 ++++++++++----------
 bash_completions_test.go          |  39 +++---
 cobra.go                          |  15 +++
 cobra/cmd/add.go                  |  13 +-
 cobra/cmd/add_test.go             |   6 +-
 cobra/cmd/golden_test.go          |  27 ----
 cobra/cmd/helpers.go              | 120 +-----------------
 cobra/cmd/helpers_test.go         |   9 ++
 cobra/cmd/init.go                 |   6 +-
 cobra/cmd/init_test.go            |   2 +-
 cobra/cmd/licenses.go             |   4 +-
 cobra/cmd/project.go              |   3 +-
 cobra/cmd/root.go                 |   8 +-
 cobra/cmd/testdata/root.go.golden |  16 +--
 cobra/tpl/main.go                 |  19 +--
 cobra_test.go                     |   6 +
 command.go                        | 112 ++++++++---------
 command_test.go                   | 199 ++++++++++++++----------------
 custom_completions.go             |   4 +-
 custom_completions_test.go        |  46 +++----
 doc/man_docs.go                   |  28 ++---
 doc/man_docs_test.go              |   8 +-
 doc/man_examples_test.go          |   4 +-
 fish_completions.go               |   6 +-
 fish_completions_test.go          |   8 +-
 powershell_completions.go         |  26 ++--
 shell_completions.md              |   7 +-
 zsh_completions.go                |   4 +-
 32 files changed, 437 insertions(+), 525 deletions(-)
 create mode 100644 .golangci.yml
 create mode 100644 cobra/cmd/helpers_test.go

diff --git a/.golangci.yml b/.golangci.yml
new file mode 100644
index 000000000..0d6e61793
--- /dev/null
+++ b/.golangci.yml
@@ -0,0 +1,48 @@
+run:
+  deadline: 5m
+
+linters:
+  disable-all: true
+  enable:
+    #- bodyclose
+    - deadcode
+    #- depguard
+    #- dogsled
+    #- dupl
+    - errcheck
+    #- exhaustive
+    #- funlen
+    - gas
+    #- gochecknoinits
+    - goconst
+    #- gocritic
+    #- gocyclo
+    #- gofmt
+    - goimports
+    - golint
+    #- gomnd
+    #- goprintffuncname
+    #- gosec
+    #- gosimple
+    - govet
+    - ineffassign
+    - interfacer
+    #- lll
+    - maligned
+    - megacheck
+    #- misspell
+    #- nakedret
+    #- noctx
+    #- nolintlint
+    #- rowserrcheck
+    #- scopelint
+    #- staticcheck
+    - structcheck
+    #- stylecheck
+    #- typecheck
+    - unconvert
+    #- unparam
+    #- unused
+    - varcheck
+    #- whitespace
+  fast: false
diff --git a/.travis.yml b/.travis.yml
index 3255e06f2..0821efdca 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,7 +1,6 @@
 language: go
 
 stages:
-  - diff
   - test
   - build
 
@@ -10,20 +9,20 @@ go:
   - 1.15.x
   - tip
 
+env: GO111MODULE=on
+
 before_install:
   - go get -u github.com/kyoh86/richgo
   - go get -u github.com/mitchellh/gox
+  - curl -sfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s -- -b $(go env GOPATH)/bin latest
 
 matrix:
   allow_failures:
     - go: tip
   include:
-    - stage: diff
-      go: 1.14.x
-      script: make fmt
     - stage: build
       go: 1.14.x
       script: make cobra_generator
 
-script: 
+script:
  - make test
diff --git a/Makefile b/Makefile
index e9740d1e1..472c73bf1 100644
--- a/Makefile
+++ b/Makefile
@@ -1,21 +1,29 @@
 BIN="./bin"
 SRC=$(shell find . -name "*.go")
 
+ifeq (, $(shell which golangci-lint))
+$(warning "could not find golangci-lint in $(PATH), run: curl -sfL https://install.goreleaser.com/github.com/golangci/golangci-lint.sh | sh")
+endif
+
 ifeq (, $(shell which richgo))
 $(warning "could not find richgo in $(PATH), run: go get github.com/kyoh86/richgo")
 endif
 
-.PHONY: fmt vet test cobra_generator install_deps clean
+.PHONY: fmt lint test cobra_generator install_deps clean
 
 default: all
 
-all: fmt vet test cobra_generator	
+all: fmt test cobra_generator
 
 fmt:
 	$(info ******************** checking formatting ********************)
 	@test -z $(shell gofmt -l $(SRC)) || (gofmt -d $(SRC); exit 1)
 
-test: install_deps vet
+lint:
+	$(info ******************** running lint tools ********************)
+	golangci-lint run -v
+
+test: install_deps lint
 	$(info ******************** running tests ********************)
 	richgo test -v ./...
 
@@ -28,9 +36,5 @@ install_deps:
 	$(info ******************** downloading dependencies ********************)
 	go get -v ./...
 
-vet:
-	$(info ******************** vetting ********************)
-	go vet ./...
-
 clean:
 	rm -rf $(BIN)
diff --git a/README.md b/README.md
index 0c48c6777..4a8811f37 100644
--- a/README.md
+++ b/README.md
@@ -234,11 +234,6 @@ func init() {
 	rootCmd.AddCommand(initCmd)
 }
 
-func er(msg interface{}) {
-	fmt.Println("Error:", msg)
-	os.Exit(1)
-}
-
 func initConfig() {
 	if cfgFile != "" {
 		// Use config file from the flag.
@@ -246,9 +241,7 @@ func initConfig() {
 	} else {
 		// Find home directory.
 		home, err := homedir.Dir()
-		if err != nil {
-			er(err)
-		}
+		cobra.CheckErr(err)
 
 		// Search config in home directory with name ".cobra" (without extension).
 		viper.AddConfigPath(home)
diff --git a/bash_completions.go b/bash_completions.go
index 846636d75..710614793 100644
--- a/bash_completions.go
+++ b/bash_completions.go
@@ -19,9 +19,9 @@ const (
 	BashCompSubdirsInDir    = "cobra_annotation_bash_completion_subdirs_in_dir"
 )
 
-func writePreamble(buf *bytes.Buffer, name string) {
-	buf.WriteString(fmt.Sprintf("# bash completion for %-36s -*- shell-script -*-\n", name))
-	buf.WriteString(fmt.Sprintf(`
+func writePreamble(buf io.StringWriter, name string) {
+	WriteStringAndCheck(buf, fmt.Sprintf("# bash completion for %-36s -*- shell-script -*-\n", name))
+	WriteStringAndCheck(buf, fmt.Sprintf(`
 __%[1]s_debug()
 {
     if [[ -n ${BASH_COMP_DEBUG_FILE} ]]; then
@@ -380,10 +380,10 @@ __%[1]s_handle_word()
 		ShellCompDirectiveFilterFileExt, ShellCompDirectiveFilterDirs))
 }
 
-func writePostscript(buf *bytes.Buffer, name string) {
+func writePostscript(buf io.StringWriter, name string) {
 	name = strings.Replace(name, ":", "__", -1)
-	buf.WriteString(fmt.Sprintf("__start_%s()\n", name))
-	buf.WriteString(fmt.Sprintf(`{
+	WriteStringAndCheck(buf, fmt.Sprintf("__start_%s()\n", name))
+	WriteStringAndCheck(buf, fmt.Sprintf(`{
     local cur prev words cword
     declare -A flaghash 2>/dev/null || :
     declare -A aliashash 2>/dev/null || :
@@ -410,33 +410,33 @@ func writePostscript(buf *bytes.Buffer, name string) {
 }
 
 `, name))
-	buf.WriteString(fmt.Sprintf(`if [[ $(type -t compopt) = "builtin" ]]; then
+	WriteStringAndCheck(buf, fmt.Sprintf(`if [[ $(type -t compopt) = "builtin" ]]; then
     complete -o default -F __start_%s %s
 else
     complete -o default -o nospace -F __start_%s %s
 fi
 
 `, name, name, name, name))
-	buf.WriteString("# ex: ts=4 sw=4 et filetype=sh\n")
+	WriteStringAndCheck(buf, "# ex: ts=4 sw=4 et filetype=sh\n")
 }
 
-func writeCommands(buf *bytes.Buffer, cmd *Command) {
-	buf.WriteString("    commands=()\n")
+func writeCommands(buf io.StringWriter, cmd *Command) {
+	WriteStringAndCheck(buf, "    commands=()\n")
 	for _, c := range cmd.Commands() {
 		if !c.IsAvailableCommand() && c != cmd.helpCommand {
 			continue
 		}
-		buf.WriteString(fmt.Sprintf("    commands+=(%q)\n", c.Name()))
+		WriteStringAndCheck(buf, fmt.Sprintf("    commands+=(%q)\n", c.Name()))
 		writeCmdAliases(buf, c)
 	}
-	buf.WriteString("\n")
+	WriteStringAndCheck(buf, "\n")
 }
 
-func writeFlagHandler(buf *bytes.Buffer, name string, annotations map[string][]string, cmd *Command) {
+func writeFlagHandler(buf io.StringWriter, name string, annotations map[string][]string, cmd *Command) {
 	for key, value := range annotations {
 		switch key {
 		case BashCompFilenameExt:
-			buf.WriteString(fmt.Sprintf("    flags_with_completion+=(%q)\n", name))
+			WriteStringAndCheck(buf, fmt.Sprintf("    flags_with_completion+=(%q)\n", name))
 
 			var ext string
 			if len(value) > 0 {
@@ -444,17 +444,18 @@ func writeFlagHandler(buf *bytes.Buffer, name string, annotations map[string][]s
 			} else {
 				ext = "_filedir"
 			}
-			buf.WriteString(fmt.Sprintf("    flags_completion+=(%q)\n", ext))
+			WriteStringAndCheck(buf, fmt.Sprintf("    flags_completion+=(%q)\n", ext))
 		case BashCompCustom:
-			buf.WriteString(fmt.Sprintf("    flags_with_completion+=(%q)\n", name))
+			WriteStringAndCheck(buf, fmt.Sprintf("    flags_with_completion+=(%q)\n", name))
+
 			if len(value) > 0 {
 				handlers := strings.Join(value, "; ")
-				buf.WriteString(fmt.Sprintf("    flags_completion+=(%q)\n", handlers))
+				WriteStringAndCheck(buf, fmt.Sprintf("    flags_completion+=(%q)\n", handlers))
 			} else {
-				buf.WriteString("    flags_completion+=(:)\n")
+				WriteStringAndCheck(buf, "    flags_completion+=(:)\n")
 			}
 		case BashCompSubdirsInDir:
-			buf.WriteString(fmt.Sprintf("    flags_with_completion+=(%q)\n", name))
+			WriteStringAndCheck(buf, fmt.Sprintf("    flags_with_completion+=(%q)\n", name))
 
 			var ext string
 			if len(value) == 1 {
@@ -462,46 +463,48 @@ func writeFlagHandler(buf *bytes.Buffer, name string, annotations map[string][]s
 			} else {
 				ext = "_filedir -d"
 			}
-			buf.WriteString(fmt.Sprintf("    flags_completion+=(%q)\n", ext))
+			WriteStringAndCheck(buf, fmt.Sprintf("    flags_completion+=(%q)\n", ext))
 		}
 	}
 }
 
-func writeShortFlag(buf *bytes.Buffer, flag *pflag.Flag, cmd *Command) {
+const cbn = "\")\n"
+
+func writeShortFlag(buf io.StringWriter, flag *pflag.Flag, cmd *Command) {
 	name := flag.Shorthand
 	format := "    "
 	if len(flag.NoOptDefVal) == 0 {
 		format += "two_word_"
 	}
-	format += "flags+=(\"-%s\")\n"
-	buf.WriteString(fmt.Sprintf(format, name))
+	format += "flags+=(\"-%s" + cbn
+	WriteStringAndCheck(buf, fmt.Sprintf(format, name))
 	writeFlagHandler(buf, "-"+name, flag.Annotations, cmd)
 }
 
-func writeFlag(buf *bytes.Buffer, flag *pflag.Flag, cmd *Command) {
+func writeFlag(buf io.StringWriter, flag *pflag.Flag, cmd *Command) {
 	name := flag.Name
 	format := "    flags+=(\"--%s"
 	if len(flag.NoOptDefVal) == 0 {
 		format += "="
 	}
-	format += "\")\n"
-	buf.WriteString(fmt.Sprintf(format, name))
+	format += cbn
+	WriteStringAndCheck(buf, fmt.Sprintf(format, name))
 	if len(flag.NoOptDefVal) == 0 {
-		format = "    two_word_flags+=(\"--%s\")\n"
-		buf.WriteString(fmt.Sprintf(format, name))
+		format = "    two_word_flags+=(\"--%s" + cbn
+		WriteStringAndCheck(buf, fmt.Sprintf(format, name))
 	}
 	writeFlagHandler(buf, "--"+name, flag.Annotations, cmd)
 }
 
-func writeLocalNonPersistentFlag(buf *bytes.Buffer, flag *pflag.Flag) {
+func writeLocalNonPersistentFlag(buf io.StringWriter, flag *pflag.Flag) {
 	name := flag.Name
-	format := "    local_nonpersistent_flags+=(\"--%[1]s\")\n"
+	format := "    local_nonpersistent_flags+=(\"--%[1]s" + cbn
 	if len(flag.NoOptDefVal) == 0 {
-		format += "    local_nonpersistent_flags+=(\"--%[1]s=\")\n"
+		format += "    local_nonpersistent_flags+=(\"--%[1]s=" + cbn
 	}
-	buf.WriteString(fmt.Sprintf(format, name))
+	WriteStringAndCheck(buf, fmt.Sprintf(format, name))
 	if len(flag.Shorthand) > 0 {
-		buf.WriteString(fmt.Sprintf("    local_nonpersistent_flags+=(\"-%s\")\n", flag.Shorthand))
+		WriteStringAndCheck(buf, fmt.Sprintf("    local_nonpersistent_flags+=(\"-%s\")\n", flag.Shorthand))
 	}
 }
 
@@ -519,9 +522,9 @@ func prepareCustomAnnotationsForFlags(cmd *Command) {
 	}
 }
 
-func writeFlags(buf *bytes.Buffer, cmd *Command) {
+func writeFlags(buf io.StringWriter, cmd *Command) {
 	prepareCustomAnnotationsForFlags(cmd)
-	buf.WriteString(`    flags=()
+	WriteStringAndCheck(buf, `    flags=()
     two_word_flags=()
     local_nonpersistent_flags=()
     flags_with_completion=()
@@ -553,11 +556,11 @@ func writeFlags(buf *bytes.Buffer, cmd *Command) {
 		}
 	})
 
-	buf.WriteString("\n")
+	WriteStringAndCheck(buf, "\n")
 }
 
-func writeRequiredFlag(buf *bytes.Buffer, cmd *Command) {
-	buf.WriteString("    must_have_one_flag=()\n")
+func writeRequiredFlag(buf io.StringWriter, cmd *Command) {
+	WriteStringAndCheck(buf, "    must_have_one_flag=()\n")
 	flags := cmd.NonInheritedFlags()
 	flags.VisitAll(func(flag *pflag.Flag) {
 		if nonCompletableFlag(flag) {
@@ -570,55 +573,55 @@ func writeRequiredFlag(buf *bytes.Buffer, cmd *Command) {
 				if flag.Value.Type() != "bool" {
 					format += "="
 				}
-				format += "\")\n"
-				buf.WriteString(fmt.Sprintf(format, flag.Name))
+				format += cbn
+				WriteStringAndCheck(buf, fmt.Sprintf(format, flag.Name))
 
 				if len(flag.Shorthand) > 0 {
-					buf.WriteString(fmt.Sprintf("    must_have_one_flag+=(\"-%s\")\n", flag.Shorthand))
+					WriteStringAndCheck(buf, fmt.Sprintf("    must_have_one_flag+=(\"-%s"+cbn, flag.Shorthand))
 				}
 			}
 		}
 	})
 }
 
-func writeRequiredNouns(buf *bytes.Buffer, cmd *Command) {
-	buf.WriteString("    must_have_one_noun=()\n")
-	sort.Sort(sort.StringSlice(cmd.ValidArgs))
+func writeRequiredNouns(buf io.StringWriter, cmd *Command) {
+	WriteStringAndCheck(buf, "    must_have_one_noun=()\n")
+	sort.Strings(cmd.ValidArgs)
 	for _, value := range cmd.ValidArgs {
 		// Remove any description that may be included following a tab character.
 		// Descriptions are not supported by bash completion.
 		value = strings.Split(value, "\t")[0]
-		buf.WriteString(fmt.Sprintf("    must_have_one_noun+=(%q)\n", value))
+		WriteStringAndCheck(buf, fmt.Sprintf("    must_have_one_noun+=(%q)\n", value))
 	}
 	if cmd.ValidArgsFunction != nil {
-		buf.WriteString("    has_completion_function=1\n")
+		WriteStringAndCheck(buf, "    has_completion_function=1\n")
 	}
 }
 
-func writeCmdAliases(buf *bytes.Buffer, cmd *Command) {
+func writeCmdAliases(buf io.StringWriter, cmd *Command) {
 	if len(cmd.Aliases) == 0 {
 		return
 	}
 
-	sort.Sort(sort.StringSlice(cmd.Aliases))
+	sort.Strings(cmd.Aliases)
 
-	buf.WriteString(fmt.Sprint(`    if [[ -z "${BASH_VERSION}" || "${BASH_VERSINFO[0]}" -gt 3 ]]; then`, "\n"))
+	WriteStringAndCheck(buf, fmt.Sprint(`    if [[ -z "${BASH_VERSION}" || "${BASH_VERSINFO[0]}" -gt 3 ]]; then`, "\n"))
 	for _, value := range cmd.Aliases {
-		buf.WriteString(fmt.Sprintf("        command_aliases+=(%q)\n", value))
-		buf.WriteString(fmt.Sprintf("        aliashash[%q]=%q\n", value, cmd.Name()))
+		WriteStringAndCheck(buf, fmt.Sprintf("        command_aliases+=(%q)\n", value))
+		WriteStringAndCheck(buf, fmt.Sprintf("        aliashash[%q]=%q\n", value, cmd.Name()))
 	}
-	buf.WriteString(`    fi`)
-	buf.WriteString("\n")
+	WriteStringAndCheck(buf, `    fi`)
+	WriteStringAndCheck(buf, "\n")
 }
-func writeArgAliases(buf *bytes.Buffer, cmd *Command) {
-	buf.WriteString("    noun_aliases=()\n")
-	sort.Sort(sort.StringSlice(cmd.ArgAliases))
+func writeArgAliases(buf io.StringWriter, cmd *Command) {
+	WriteStringAndCheck(buf, "    noun_aliases=()\n")
+	sort.Strings(cmd.ArgAliases)
 	for _, value := range cmd.ArgAliases {
-		buf.WriteString(fmt.Sprintf("    noun_aliases+=(%q)\n", value))
+		WriteStringAndCheck(buf, fmt.Sprintf("    noun_aliases+=(%q)\n", value))
 	}
 }
 
-func gen(buf *bytes.Buffer, cmd *Command) {
+func gen(buf io.StringWriter, cmd *Command) {
 	for _, c := range cmd.Commands() {
 		if !c.IsAvailableCommand() && c != cmd.helpCommand {
 			continue
@@ -630,22 +633,22 @@ func gen(buf *bytes.Buffer, cmd *Command) {
 	commandName = strings.Replace(commandName, ":", "__", -1)
 
 	if cmd.Root() == cmd {
-		buf.WriteString(fmt.Sprintf("_%s_root_command()\n{\n", commandName))
+		WriteStringAndCheck(buf, fmt.Sprintf("_%s_root_command()\n{\n", commandName))
 	} else {
-		buf.WriteString(fmt.Sprintf("_%s()\n{\n", commandName))
+		WriteStringAndCheck(buf, fmt.Sprintf("_%s()\n{\n", commandName))
 	}
 
-	buf.WriteString(fmt.Sprintf("    last_command=%q\n", commandName))
-	buf.WriteString("\n")
-	buf.WriteString("    command_aliases=()\n")
-	buf.WriteString("\n")
+	WriteStringAndCheck(buf, fmt.Sprintf("    last_command=%q\n", commandName))
+	WriteStringAndCheck(buf, "\n")
+	WriteStringAndCheck(buf, "    command_aliases=()\n")
+	WriteStringAndCheck(buf, "\n")
 
 	writeCommands(buf, cmd)
 	writeFlags(buf, cmd)
 	writeRequiredFlag(buf, cmd)
 	writeRequiredNouns(buf, cmd)
 	writeArgAliases(buf, cmd)
-	buf.WriteString("}\n\n")
+	WriteStringAndCheck(buf, "}\n\n")
 }
 
 // GenBashCompletion generates bash completion file and writes to the passed writer.
diff --git a/bash_completions_test.go b/bash_completions_test.go
index 2c182ba73..21d1fe0eb 100644
--- a/bash_completions_test.go
+++ b/bash_completions_test.go
@@ -40,10 +40,9 @@ func checkRegex(t *testing.T, found, pattern string) {
 }
 
 func runShellCheck(s string) error {
-	excluded := []string{
+	cmd := exec.Command("shellcheck", "-s", "bash", "-", "-e",
 		"SC2034", // PREFIX appears unused. Verify it or export it.
-	}
-	cmd := exec.Command("shellcheck", "-s", "bash", "-", "-e", strings.Join(excluded, ","))
+	)
 	cmd.Stderr = os.Stderr
 	cmd.Stdout = os.Stdout
 
@@ -52,7 +51,9 @@ func runShellCheck(s string) error {
 		return err
 	}
 	go func() {
-		stdin.Write([]byte(s))
+		_, err := stdin.Write([]byte(s))
+		CheckErr(err)
+
 		stdin.Close()
 	}()
 
@@ -74,26 +75,26 @@ func TestBashCompletions(t *testing.T) {
 		Run:                    emptyRun,
 	}
 	rootCmd.Flags().IntP("introot", "i", -1, "help message for flag introot")
-	rootCmd.MarkFlagRequired("introot")
+	assertNoErr(t, rootCmd.MarkFlagRequired("introot"))
 
 	// Filename.
 	rootCmd.Flags().String("filename", "", "Enter a filename")
-	rootCmd.MarkFlagFilename("filename", "json", "yaml", "yml")
+	assertNoErr(t, rootCmd.MarkFlagFilename("filename", "json", "yaml", "yml"))
 
 	// Persistent filename.
 	rootCmd.PersistentFlags().String("persistent-filename", "", "Enter a filename")
-	rootCmd.MarkPersistentFlagFilename("persistent-filename")
-	rootCmd.MarkPersistentFlagRequired("persistent-filename")
+	assertNoErr(t, rootCmd.MarkPersistentFlagFilename("persistent-filename"))
+	assertNoErr(t, rootCmd.MarkPersistentFlagRequired("persistent-filename"))
 
 	// Filename extensions.
 	rootCmd.Flags().String("filename-ext", "", "Enter a filename (extension limited)")
-	rootCmd.MarkFlagFilename("filename-ext")
+	assertNoErr(t, rootCmd.MarkFlagFilename("filename-ext"))
 	rootCmd.Flags().String("custom", "", "Enter a filename (extension limited)")
-	rootCmd.MarkFlagCustom("custom", "__complete_custom")
+	assertNoErr(t, rootCmd.MarkFlagCustom("custom", "__complete_custom"))
 
 	// Subdirectories in a given directory.
 	rootCmd.Flags().String("theme", "", "theme to use (located in /themes/THEMENAME/)")
-	rootCmd.Flags().SetAnnotation("theme", BashCompSubdirsInDir, []string{"themes"})
+	assertNoErr(t, rootCmd.Flags().SetAnnotation("theme", BashCompSubdirsInDir, []string{"themes"}))
 
 	// For two word flags check
 	rootCmd.Flags().StringP("two", "t", "", "this is two word flags")
@@ -109,9 +110,9 @@ func TestBashCompletions(t *testing.T) {
 	}
 
 	echoCmd.Flags().String("filename", "", "Enter a filename")
-	echoCmd.MarkFlagFilename("filename", "json", "yaml", "yml")
+	assertNoErr(t, echoCmd.MarkFlagFilename("filename", "json", "yaml", "yml"))
 	echoCmd.Flags().String("config", "", "config to use (located in /config/PROFILE/)")
-	echoCmd.Flags().SetAnnotation("config", BashCompSubdirsInDir, []string{"config"})
+	assertNoErr(t, echoCmd.Flags().SetAnnotation("config", BashCompSubdirsInDir, []string{"config"}))
 
 	printCmd := &Command{
 		Use:   "print [string to print]",
@@ -149,7 +150,7 @@ func TestBashCompletions(t *testing.T) {
 	rootCmd.AddCommand(echoCmd, printCmd, deprecatedCmd, colonCmd)
 
 	buf := new(bytes.Buffer)
-	rootCmd.GenBashCompletion(buf)
+	assertNoErr(t, rootCmd.GenBashCompletion(buf))
 	output := buf.String()
 
 	check(t, output, "_root")
@@ -216,10 +217,10 @@ func TestBashCompletionHiddenFlag(t *testing.T) {
 
 	const flagName = "hiddenFlag"
 	c.Flags().Bool(flagName, false, "")
-	c.Flags().MarkHidden(flagName)
+	assertNoErr(t, c.Flags().MarkHidden(flagName))
 
 	buf := new(bytes.Buffer)
-	c.GenBashCompletion(buf)
+	assertNoErr(t, c.GenBashCompletion(buf))
 	output := buf.String()
 
 	if strings.Contains(output, flagName) {
@@ -232,10 +233,10 @@ func TestBashCompletionDeprecatedFlag(t *testing.T) {
 
 	const flagName = "deprecated-flag"
 	c.Flags().Bool(flagName, false, "")
-	c.Flags().MarkDeprecated(flagName, "use --not-deprecated instead")
+	assertNoErr(t, c.Flags().MarkDeprecated(flagName, "use --not-deprecated instead"))
 
 	buf := new(bytes.Buffer)
-	c.GenBashCompletion(buf)
+	assertNoErr(t, c.GenBashCompletion(buf))
 	output := buf.String()
 
 	if strings.Contains(output, flagName) {
@@ -250,7 +251,7 @@ func TestBashCompletionTraverseChildren(t *testing.T) {
 	c.Flags().BoolP("bool-flag", "b", false, "bool flag")
 
 	buf := new(bytes.Buffer)
-	c.GenBashCompletion(buf)
+	assertNoErr(t, c.GenBashCompletion(buf))
 	output := buf.String()
 
 	// check that local nonpersistent flag are not set since we have TraverseChildren set to true
diff --git a/cobra.go b/cobra.go
index d01becc8f..d6cbfd719 100644
--- a/cobra.go
+++ b/cobra.go
@@ -19,6 +19,7 @@ package cobra
 import (
 	"fmt"
 	"io"
+	"os"
 	"reflect"
 	"strconv"
 	"strings"
@@ -205,3 +206,17 @@ func stringInSlice(a string, list []string) bool {
 	}
 	return false
 }
+
+// CheckErr prints the msg with the prefix 'Error:' and exits with error code 1. If the msg is nil, it does nothing.
+func CheckErr(msg interface{}) {
+	if msg != nil {
+		fmt.Fprintln(os.Stderr, "Error:", msg)
+		os.Exit(1)
+	}
+}
+
+// WriteStringAndCheck writes a string into a buffer, and checks if the error is not nil.
+func WriteStringAndCheck(b io.StringWriter, s string) {
+	_, err := b.WriteString(s)
+	CheckErr(err)
+}
diff --git a/cobra/cmd/add.go b/cobra/cmd/add.go
index 6645a755f..8377411ed 100644
--- a/cobra/cmd/add.go
+++ b/cobra/cmd/add.go
@@ -40,13 +40,11 @@ Example: cobra add server -> resulting in a new cmd/server.go`,
 
 		Run: func(cmd *cobra.Command, args []string) {
 			if len(args) < 1 {
-				er("add needs a name for the command")
+				cobra.CheckErr(fmt.Errorf("add needs a name for the command"))
 			}
 
 			wd, err := os.Getwd()
-			if err != nil {
-				er(err)
-			}
+			cobra.CheckErr(err)
 
 			commandName := validateCmdName(args[0])
 			command := &Command{
@@ -59,10 +57,7 @@ Example: cobra add server -> resulting in a new cmd/server.go`,
 				},
 			}
 
-			err = command.Create()
-			if err != nil {
-				er(err)
-			}
+			cobra.CheckErr(command.Create())
 
 			fmt.Printf("%s created at %s\n", command.CmdName, command.AbsolutePath)
 		},
@@ -72,7 +67,7 @@ Example: cobra add server -> resulting in a new cmd/server.go`,
 func init() {
 	addCmd.Flags().StringVarP(&packageName, "package", "t", "", "target package name (e.g. github.com/spf13/hugo)")
 	addCmd.Flags().StringVarP(&parentName, "parent", "p", "rootCmd", "variable name of parent command for this command")
-	addCmd.Flags().MarkDeprecated("package", "this operation has been removed.")
+	cobra.CheckErr(addCmd.Flags().MarkDeprecated("package", "this operation has been removed."))
 }
 
 // validateCmdName returns source without any dashes and underscore.
diff --git a/cobra/cmd/add_test.go b/cobra/cmd/add_test.go
index de92fcea6..0b32ca67e 100644
--- a/cobra/cmd/add_test.go
+++ b/cobra/cmd/add_test.go
@@ -14,10 +14,8 @@ func TestGoldenAddCmd(t *testing.T) {
 	}
 	defer os.RemoveAll(command.AbsolutePath)
 
-	command.Project.Create()
-	if err := command.Create(); err != nil {
-		t.Fatal(err)
-	}
+	assertNoErr(t, command.Project.Create())
+	assertNoErr(t, command.Create())
 
 	generatedFile := fmt.Sprintf("%s/cmd/%s.go", command.AbsolutePath, command.CmdName)
 	goldenFile := fmt.Sprintf("testdata/%s.go.golden", command.CmdName)
diff --git a/cobra/cmd/golden_test.go b/cobra/cmd/golden_test.go
index e4055f33f..99b92e31b 100644
--- a/cobra/cmd/golden_test.go
+++ b/cobra/cmd/golden_test.go
@@ -3,14 +3,11 @@ package cmd
 import (
 	"bytes"
 	"errors"
-	"flag"
 	"fmt"
 	"io/ioutil"
 	"os/exec"
 )
 
-var update = flag.Bool("update", false, "update .golden files")
-
 func init() {
 	// Mute commands.
 	addCmd.SetOut(new(bytes.Buffer))
@@ -58,27 +55,3 @@ func compareFiles(pathA, pathB string) error {
 	}
 	return nil
 }
-
-// checkLackFiles checks if all elements of expected are in got.
-func checkLackFiles(expected, got []string) error {
-	lacks := make([]string, 0, len(expected))
-	for _, ev := range expected {
-		if !stringInStringSlice(ev, got) {
-			lacks = append(lacks, ev)
-		}
-	}
-	if len(lacks) > 0 {
-		return fmt.Errorf("Lack %v file(s): %v", len(lacks), lacks)
-	}
-	return nil
-}
-
-// stringInStringSlice checks if s is an element of slice.
-func stringInStringSlice(s string, slice []string) bool {
-	for _, v := range slice {
-		if s == v {
-			return true
-		}
-	}
-	return false
-}
diff --git a/cobra/cmd/helpers.go b/cobra/cmd/helpers.go
index cd94b3e31..6a8047e38 100644
--- a/cobra/cmd/helpers.go
+++ b/cobra/cmd/helpers.go
@@ -14,14 +14,12 @@
 package cmd
 
 import (
-	"bytes"
-	"fmt"
-	"io"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"strings"
-	"text/template"
+
+	"github.com/spf13/cobra"
 )
 
 var srcPaths []string
@@ -43,14 +41,12 @@ func init() {
 		}
 
 		out, err := exec.Command(goExecutable, "env", "GOPATH").Output()
-		if err != nil {
-			er(err)
-		}
+		cobra.CheckErr(err)
 
 		toolchainGoPath := strings.TrimSpace(string(out))
 		goPaths = filepath.SplitList(toolchainGoPath)
 		if len(goPaths) == 0 {
-			er("$GOPATH is not set")
+			cobra.CheckErr("$GOPATH is not set")
 		}
 	}
 	srcPaths = make([]string, 0, len(goPaths))
@@ -58,111 +54,3 @@ func init() {
 		srcPaths = append(srcPaths, filepath.Join(goPath, "src"))
 	}
 }
-
-func er(msg interface{}) {
-	fmt.Println("Error:", msg)
-	os.Exit(1)
-}
-
-// isEmpty checks if a given path is empty.
-// Hidden files in path are ignored.
-func isEmpty(path string) bool {
-	fi, err := os.Stat(path)
-	if err != nil {
-		er(err)
-	}
-
-	if !fi.IsDir() {
-		return fi.Size() == 0
-	}
-
-	f, err := os.Open(path)
-	if err != nil {
-		er(err)
-	}
-	defer f.Close()
-
-	names, err := f.Readdirnames(-1)
-	if err != nil && err != io.EOF {
-		er(err)
-	}
-
-	for _, name := range names {
-		if len(name) > 0 && name[0] != '.' {
-			return false
-		}
-	}
-	return true
-}
-
-// exists checks if a file or directory exists.
-func exists(path string) bool {
-	if path == "" {
-		return false
-	}
-	_, err := os.Stat(path)
-	if err == nil {
-		return true
-	}
-	if !os.IsNotExist(err) {
-		er(err)
-	}
-	return false
-}
-
-func executeTemplate(tmplStr string, data interface{}) (string, error) {
-	tmpl, err := template.New("").Funcs(template.FuncMap{"comment": commentifyString}).Parse(tmplStr)
-	if err != nil {
-		return "", err
-	}
-
-	buf := new(bytes.Buffer)
-	err = tmpl.Execute(buf, data)
-	return buf.String(), err
-}
-
-func writeStringToFile(path string, s string) error {
-	return writeToFile(path, strings.NewReader(s))
-}
-
-// writeToFile writes r to file with path only
-// if file/directory on given path doesn't exist.
-func writeToFile(path string, r io.Reader) error {
-	if exists(path) {
-		return fmt.Errorf("%v already exists", path)
-	}
-
-	dir := filepath.Dir(path)
-	if dir != "" {
-		if err := os.MkdirAll(dir, 0777); err != nil {
-			return err
-		}
-	}
-
-	file, err := os.Create(path)
-	if err != nil {
-		return err
-	}
-	defer file.Close()
-
-	_, err = io.Copy(file, r)
-	return err
-}
-
-// commentfyString comments every line of in.
-func commentifyString(in string) string {
-	var newlines []string
-	lines := strings.Split(in, "\n")
-	for _, line := range lines {
-		if strings.HasPrefix(line, "//") {
-			newlines = append(newlines, line)
-		} else {
-			if line == "" {
-				newlines = append(newlines, "//")
-			} else {
-				newlines = append(newlines, "// "+line)
-			}
-		}
-	}
-	return strings.Join(newlines, "\n")
-}
diff --git a/cobra/cmd/helpers_test.go b/cobra/cmd/helpers_test.go
new file mode 100644
index 000000000..c5d20026c
--- /dev/null
+++ b/cobra/cmd/helpers_test.go
@@ -0,0 +1,9 @@
+package cmd
+
+import "testing"
+
+func assertNoErr(t *testing.T, e error) {
+	if e != nil {
+		t.Error(e)
+	}
+}
diff --git a/cobra/cmd/init.go b/cobra/cmd/init.go
index 504a47850..8c0e617ab 100644
--- a/cobra/cmd/init.go
+++ b/cobra/cmd/init.go
@@ -39,9 +39,7 @@ and the appropriate structure for a Cobra-based CLI application.
 		Run: func(_ *cobra.Command, args []string) {
 
 			projectPath, err := initializeProject(args)
-			if err != nil {
-				er(err)
-			}
+			cobra.CheckErr(err)
 			fmt.Printf("Your Cobra application is ready at\n%s\n", projectPath)
 		},
 	}
@@ -49,7 +47,7 @@ and the appropriate structure for a Cobra-based CLI application.
 
 func init() {
 	initCmd.Flags().StringVar(&pkgName, "pkg-name", "", "fully qualified pkg name")
-	initCmd.MarkFlagRequired("pkg-name")
+	cobra.CheckErr(initCmd.MarkFlagRequired("pkg-name"))
 }
 
 func initializeProject(args []string) (string, error) {
diff --git a/cobra/cmd/init_test.go b/cobra/cmd/init_test.go
index c4b3f09a2..6d21ef773 100644
--- a/cobra/cmd/init_test.go
+++ b/cobra/cmd/init_test.go
@@ -59,7 +59,7 @@ func TestGoldenInitCmd(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 
-			initCmd.Flags().Set("pkg-name", tt.pkgName)
+			assertNoErr(t, initCmd.Flags().Set("pkg-name", tt.pkgName))
 			viper.Set("useViper", true)
 			projectPath, err := initializeProject(tt.args)
 			defer func() {
diff --git a/cobra/cmd/licenses.go b/cobra/cmd/licenses.go
index a070134dd..2b3a42438 100644
--- a/cobra/cmd/licenses.go
+++ b/cobra/cmd/licenses.go
@@ -16,9 +16,11 @@
 package cmd
 
 import (
+	"fmt"
 	"strings"
 	"time"
 
+	"github.com/spf13/cobra"
 	"github.com/spf13/viper"
 )
 
@@ -92,7 +94,7 @@ func copyrightLine() string {
 func findLicense(name string) License {
 	found := matchLicense(name)
 	if found == "" {
-		er("unknown license: " + name)
+		cobra.CheckErr(fmt.Errorf("unknown license: " + name))
 	}
 	return Licenses[found]
 }
diff --git a/cobra/cmd/project.go b/cobra/cmd/project.go
index ecd783d03..bd68a31d7 100644
--- a/cobra/cmd/project.go
+++ b/cobra/cmd/project.go
@@ -5,6 +5,7 @@ import (
 	"os"
 	"text/template"
 
+	"github.com/spf13/cobra"
 	"github.com/spf13/cobra/cobra/tpl"
 )
 
@@ -49,7 +50,7 @@ func (p *Project) Create() error {
 
 	// create cmd/root.go
 	if _, err = os.Stat(fmt.Sprintf("%s/cmd", p.AbsolutePath)); os.IsNotExist(err) {
-		os.Mkdir(fmt.Sprintf("%s/cmd", p.AbsolutePath), 0751)
+		cobra.CheckErr(os.Mkdir(fmt.Sprintf("%s/cmd", p.AbsolutePath), 0751))
 	}
 	rootFile, err := os.Create(fmt.Sprintf("%s/cmd/root.go", p.AbsolutePath))
 	if err != nil {
diff --git a/cobra/cmd/root.go b/cobra/cmd/root.go
index 97f404bbb..f27ae7e6c 100644
--- a/cobra/cmd/root.go
+++ b/cobra/cmd/root.go
@@ -47,8 +47,8 @@ func init() {
 	rootCmd.PersistentFlags().StringP("author", "a", "YOUR NAME", "author name for copyright attribution")
 	rootCmd.PersistentFlags().StringVarP(&userLicense, "license", "l", "", "name of license for the project")
 	rootCmd.PersistentFlags().Bool("viper", true, "use Viper for configuration")
-	viper.BindPFlag("author", rootCmd.PersistentFlags().Lookup("author"))
-	viper.BindPFlag("useViper", rootCmd.PersistentFlags().Lookup("viper"))
+	cobra.CheckErr(viper.BindPFlag("author", rootCmd.PersistentFlags().Lookup("author")))
+	cobra.CheckErr(viper.BindPFlag("useViper", rootCmd.PersistentFlags().Lookup("viper")))
 	viper.SetDefault("author", "NAME HERE <EMAIL ADDRESS>")
 	viper.SetDefault("license", "apache")
 
@@ -63,9 +63,7 @@ func initConfig() {
 	} else {
 		// Find home directory.
 		home, err := homedir.Dir()
-		if err != nil {
-			er(err)
-		}
+		cobra.CheckErr(err)
 
 		// Search config in home directory with name ".cobra" (without extension).
 		viper.AddConfigPath(home)
diff --git a/cobra/cmd/testdata/root.go.golden b/cobra/cmd/testdata/root.go.golden
index 260c7aa81..be040365b 100644
--- a/cobra/cmd/testdata/root.go.golden
+++ b/cobra/cmd/testdata/root.go.golden
@@ -17,8 +17,8 @@ package cmd
 
 import (
 	"fmt"
-	"github.com/spf13/cobra"
 	"os"
+	"github.com/spf13/cobra"
 
 	homedir "github.com/mitchellh/go-homedir"
 	"github.com/spf13/viper"
@@ -38,16 +38,13 @@ This application is a tool to generate the needed files
 to quickly create a Cobra application.`,
 	// Uncomment the following line if your bare application
 	// has an action associated with it:
-	//	Run: func(cmd *cobra.Command, args []string) { },
+	// Run: func(cmd *cobra.Command, args []string) { },
 }
 
 // Execute adds all child commands to the root command and sets flags appropriately.
 // This is called by main.main(). It only needs to happen once to the rootCmd.
 func Execute() {
-	if err := rootCmd.Execute(); err != nil {
-		fmt.Println(err)
-		os.Exit(1)
-	}
+	cobra.CheckErr(rootCmd.Execute())
 }
 
 func init() {
@@ -72,10 +69,7 @@ func initConfig() {
 	} else {
 		// Find home directory.
 		home, err := homedir.Dir()
-		if err != nil {
-			fmt.Println(err)
-			os.Exit(1)
-		}
+		cobra.CheckErr(err)
 
 		// Search config in home directory with name ".testproject" (without extension).
 		viper.AddConfigPath(home)
@@ -86,6 +80,6 @@ func initConfig() {
 
 	// If a config file is found, read it in.
 	if err := viper.ReadInConfig(); err == nil {
-		fmt.Println("Using config file:", viper.ConfigFileUsed())
+		fmt.Fprintln(os.Stderr, "Using config file:", viper.ConfigFileUsed())
 	}
 }
diff --git a/cobra/tpl/main.go b/cobra/tpl/main.go
index 4348e5616..0b9c6610e 100644
--- a/cobra/tpl/main.go
+++ b/cobra/tpl/main.go
@@ -24,12 +24,11 @@ package cmd
 
 import (
 	"fmt"
-	"github.com/spf13/cobra"
 	"os"
+	"github.com/spf13/cobra"
 {{ if .Viper }}
 	homedir "github.com/mitchellh/go-homedir"
-	"github.com/spf13/viper"
-{{ end -}}
+	"github.com/spf13/viper"{{ end }}
 )
 
 {{ if .Viper -}}
@@ -48,16 +47,13 @@ This application is a tool to generate the needed files
 to quickly create a Cobra application.` + "`" + `,
 	// Uncomment the following line if your bare application
 	// has an action associated with it:
-	//	Run: func(cmd *cobra.Command, args []string) { },
+	// Run: func(cmd *cobra.Command, args []string) { },
 }
 
 // Execute adds all child commands to the root command and sets flags appropriately.
 // This is called by main.main(). It only needs to happen once to the rootCmd.
 func Execute() {
-	if err := rootCmd.Execute(); err != nil {
-		fmt.Println(err)
-		os.Exit(1)
-	}
+	cobra.CheckErr(rootCmd.Execute())
 }
 
 func init() {
@@ -86,10 +82,7 @@ func initConfig() {
 	} else {
 		// Find home directory.
 		home, err := homedir.Dir()
-		if err != nil {
-			fmt.Println(err)
-			os.Exit(1)
-		}
+		cobra.CheckErr(err)
 
 		// Search config in home directory with name ".{{ .AppName }}" (without extension).
 		viper.AddConfigPath(home)
@@ -100,7 +93,7 @@ func initConfig() {
 
 	// If a config file is found, read it in.
 	if err := viper.ReadInConfig(); err == nil {
-		fmt.Println("Using config file:", viper.ConfigFileUsed())
+		fmt.Fprintln(os.Stderr, "Using config file:", viper.ConfigFileUsed())
 	}
 }
 {{- end }}
diff --git a/cobra_test.go b/cobra_test.go
index 0d1755bdb..1219cc079 100644
--- a/cobra_test.go
+++ b/cobra_test.go
@@ -5,6 +5,12 @@ import (
 	"text/template"
 )
 
+func assertNoErr(t *testing.T, e error) {
+	if e != nil {
+		t.Error(e)
+	}
+}
+
 func TestAddTemplateFunctions(t *testing.T) {
 	AddTemplateFunc("t", func() bool { return true })
 	AddTemplateFuncs(template.FuncMap{
diff --git a/command.go b/command.go
index 2b82a553d..d6732ad11 100644
--- a/command.go
+++ b/command.go
@@ -84,9 +84,6 @@ type Command struct {
 	// Deprecated defines, if this command is deprecated and should print this string when used.
 	Deprecated string
 
-	// Hidden defines, if this command is hidden and should NOT show up in the list of available commands.
-	Hidden bool
-
 	// Annotations are key/value pairs that can be used by applications to identify or
 	// group commands.
 	Annotations map[string]string
@@ -126,55 +123,6 @@ type Command struct {
 	// PersistentPostRunE: PersistentPostRun but returns an error.
 	PersistentPostRunE func(cmd *Command, args []string) error
 
-	// SilenceErrors is an option to quiet errors down stream.
-	SilenceErrors bool
-
-	// SilenceUsage is an option to silence usage when an error occurs.
-	SilenceUsage bool
-
-	// DisableFlagParsing disables the flag parsing.
-	// If this is true all flags will be passed to the command as arguments.
-	DisableFlagParsing bool
-
-	// DisableAutoGenTag defines, if gen tag ("Auto generated by spf13/cobra...")
-	// will be printed by generating docs for this command.
-	DisableAutoGenTag bool
-
-	// DisableFlagsInUseLine will disable the addition of [flags] to the usage
-	// line of a command when printing help or generating docs
-	DisableFlagsInUseLine bool
-
-	// DisableSuggestions disables the suggestions based on Levenshtein distance
-	// that go along with 'unknown command' messages.
-	DisableSuggestions bool
-	// SuggestionsMinimumDistance defines minimum levenshtein distance to display suggestions.
-	// Must be > 0.
-	SuggestionsMinimumDistance int
-
-	// TraverseChildren parses flags on all parents before executing child command.
-	TraverseChildren bool
-
-	// FParseErrWhitelist flag parse errors to be ignored
-	FParseErrWhitelist FParseErrWhitelist
-
-	ctx context.Context
-
-	// commands is the list of commands supported by this program.
-	commands []*Command
-	// parent is a parent command for this command.
-	parent *Command
-	// Max lengths of commands' string lengths for use in padding.
-	commandsMaxUseLen         int
-	commandsMaxCommandPathLen int
-	commandsMaxNameLen        int
-	// commandsAreSorted defines, if command slice are sorted or not.
-	commandsAreSorted bool
-	// commandCalledAs is the name or alias value used to call this command.
-	commandCalledAs struct {
-		name   string
-		called bool
-	}
-
 	// args is actual args parsed from flags.
 	args []string
 	// flagErrorBuf contains all error messages from pflag.
@@ -216,6 +164,60 @@ type Command struct {
 	outWriter io.Writer
 	// errWriter is a writer defined by the user that replaces stderr
 	errWriter io.Writer
+
+	//FParseErrWhitelist flag parse errors to be ignored
+	FParseErrWhitelist FParseErrWhitelist
+
+	// commandsAreSorted defines, if command slice are sorted or not.
+	commandsAreSorted bool
+	// commandCalledAs is the name or alias value used to call this command.
+	commandCalledAs struct {
+		name   string
+		called bool
+	}
+
+	ctx context.Context
+
+	// commands is the list of commands supported by this program.
+	commands []*Command
+	// parent is a parent command for this command.
+	parent *Command
+	// Max lengths of commands' string lengths for use in padding.
+	commandsMaxUseLen         int
+	commandsMaxCommandPathLen int
+	commandsMaxNameLen        int
+
+	// TraverseChildren parses flags on all parents before executing child command.
+	TraverseChildren bool
+
+	// Hidden defines, if this command is hidden and should NOT show up in the list of available commands.
+	Hidden bool
+
+	// SilenceErrors is an option to quiet errors down stream.
+	SilenceErrors bool
+
+	// SilenceUsage is an option to silence usage when an error occurs.
+	SilenceUsage bool
+
+	// DisableFlagParsing disables the flag parsing.
+	// If this is true all flags will be passed to the command as arguments.
+	DisableFlagParsing bool
+
+	// DisableAutoGenTag defines, if gen tag ("Auto generated by spf13/cobra...")
+	// will be printed by generating docs for this command.
+	DisableAutoGenTag bool
+
+	// DisableFlagsInUseLine will disable the addition of [flags] to the usage
+	// line of a command when printing help or generating docs
+	DisableFlagsInUseLine bool
+
+	// DisableSuggestions disables the suggestions based on Levenshtein distance
+	// that go along with 'unknown command' messages.
+	DisableSuggestions bool
+
+	// SuggestionsMinimumDistance defines minimum levenshtein distance to display suggestions.
+	// Must be > 0.
+	SuggestionsMinimumDistance int
 }
 
 // Context returns underlying command context. If command wasn't
@@ -418,7 +420,7 @@ func (c *Command) UsageString() string {
 	c.outWriter = bb
 	c.errWriter = bb
 
-	c.Usage()
+	CheckErr(c.Usage())
 
 	// Setting things back to normal
 	c.outWriter = tmpOutput
@@ -1087,10 +1089,10 @@ Simply type ` + c.Name() + ` help [path to command] for full details.`,
 				cmd, _, e := c.Root().Find(args)
 				if cmd == nil || e != nil {
 					c.Printf("Unknown help topic %#q\n", args)
-					c.Root().Usage()
+					CheckErr(c.Root().Usage())
 				} else {
 					cmd.InitDefaultHelpFlag() // make possible 'help' flag to be shown
-					cmd.Help()
+					CheckErr(cmd.Help())
 				}
 			},
 		}
diff --git a/command_test.go b/command_test.go
index 3a47a81b3..9640fc5dc 100644
--- a/command_test.go
+++ b/command_test.go
@@ -58,6 +58,8 @@ func checkStringOmits(t *testing.T, got, expected string) {
 	}
 }
 
+const onetwo = "one two"
+
 func TestSingleCommand(t *testing.T) {
 	var rootCmdArgs []string
 	rootCmd := &Command{
@@ -78,9 +80,8 @@ func TestSingleCommand(t *testing.T) {
 	}
 
 	got := strings.Join(rootCmdArgs, " ")
-	expected := "one two"
-	if got != expected {
-		t.Errorf("rootCmdArgs expected: %q, got: %q", expected, got)
+	if got != onetwo {
+		t.Errorf("rootCmdArgs expected: %q, got: %q", onetwo, got)
 	}
 }
 
@@ -104,9 +105,8 @@ func TestChildCommand(t *testing.T) {
 	}
 
 	got := strings.Join(child1CmdArgs, " ")
-	expected := "one two"
-	if got != expected {
-		t.Errorf("child1CmdArgs expected: %q, got: %q", expected, got)
+	if got != onetwo {
+		t.Errorf("child1CmdArgs expected: %q, got: %q", onetwo, got)
 	}
 }
 
@@ -145,7 +145,7 @@ func TestSubcommandExecuteC(t *testing.T) {
 	}
 
 	if c.Name() != "child" {
-		t.Errorf(`invalid command returned from ExecuteC: expected "child"', got %q`, c.Name())
+		t.Errorf(`invalid command returned from ExecuteC: expected "child"', got: %q`, c.Name())
 	}
 }
 
@@ -243,9 +243,8 @@ func TestCommandAlias(t *testing.T) {
 	}
 
 	got := strings.Join(timesCmdArgs, " ")
-	expected := "one two"
-	if got != expected {
-		t.Errorf("timesCmdArgs expected: %v, got: %v", expected, got)
+	if got != onetwo {
+		t.Errorf("timesCmdArgs expected: %v, got: %v", onetwo, got)
 	}
 }
 
@@ -271,9 +270,8 @@ func TestEnablePrefixMatching(t *testing.T) {
 	}
 
 	got := strings.Join(aCmdArgs, " ")
-	expected := "one two"
-	if got != expected {
-		t.Errorf("aCmdArgs expected: %q, got: %q", expected, got)
+	if got != onetwo {
+		t.Errorf("aCmdArgs expected: %q, got: %q", onetwo, got)
 	}
 
 	EnablePrefixMatching = false
@@ -307,9 +305,8 @@ func TestAliasPrefixMatching(t *testing.T) {
 	}
 
 	got := strings.Join(timesCmdArgs, " ")
-	expected := "one two"
-	if got != expected {
-		t.Errorf("timesCmdArgs expected: %v, got: %v", expected, got)
+	if got != onetwo {
+		t.Errorf("timesCmdArgs expected: %v, got: %v", onetwo, got)
 	}
 
 	EnablePrefixMatching = false
@@ -338,9 +335,8 @@ func TestChildSameName(t *testing.T) {
 	}
 
 	got := strings.Join(fooCmdArgs, " ")
-	expected := "one two"
-	if got != expected {
-		t.Errorf("fooCmdArgs expected: %v, got: %v", expected, got)
+	if got != onetwo {
+		t.Errorf("fooCmdArgs expected: %v, got: %v", onetwo, got)
 	}
 }
 
@@ -368,9 +364,8 @@ func TestGrandChildSameName(t *testing.T) {
 	}
 
 	got := strings.Join(fooCmdArgs, " ")
-	expected := "one two"
-	if got != expected {
-		t.Errorf("fooCmdArgs expected: %v, got: %v", expected, got)
+	if got != onetwo {
+		t.Errorf("fooCmdArgs expected: %v, got: %v", onetwo, got)
 	}
 }
 
@@ -406,9 +401,8 @@ func TestFlagLong(t *testing.T) {
 	}
 
 	got := strings.Join(cArgs, " ")
-	expected := "one two"
-	if got != expected {
-		t.Errorf("Expected arguments: %q, got %q", expected, got)
+	if got != onetwo {
+		t.Errorf("rootCmdArgs expected: %q, got: %q", onetwo, got)
 	}
 }
 
@@ -441,9 +435,8 @@ func TestFlagShort(t *testing.T) {
 	}
 
 	got := strings.Join(cArgs, " ")
-	expected := "one two"
-	if got != expected {
-		t.Errorf("Expected arguments: %q, got %q", expected, got)
+	if got != onetwo {
+		t.Errorf("rootCmdArgs expected: %q, got: %q", onetwo, got)
 	}
 }
 
@@ -645,9 +638,8 @@ func TestPersistentFlagsOnSameCommand(t *testing.T) {
 	}
 
 	got := strings.Join(rootCmdArgs, " ")
-	expected := "one two"
-	if got != expected {
-		t.Errorf("rootCmdArgs expected: %q, got %q", expected, got)
+	if got != onetwo {
+		t.Errorf("rootCmdArgs expected: %q, got %q", onetwo, got)
 	}
 	if flagValue != 7 {
 		t.Errorf("flagValue expected: %v, got %v", 7, flagValue)
@@ -731,9 +723,8 @@ func TestPersistentFlagsOnChild(t *testing.T) {
 	}
 
 	got := strings.Join(childCmdArgs, " ")
-	expected := "one two"
-	if got != expected {
-		t.Errorf("childCmdArgs expected: %q, got %q", expected, got)
+	if got != onetwo {
+		t.Errorf("rootCmdArgs expected: %q, got: %q", onetwo, got)
 	}
 	if parentFlagValue != 8 {
 		t.Errorf("parentFlagValue expected: %v, got %v", 8, parentFlagValue)
@@ -746,9 +737,9 @@ func TestPersistentFlagsOnChild(t *testing.T) {
 func TestRequiredFlags(t *testing.T) {
 	c := &Command{Use: "c", Run: emptyRun}
 	c.Flags().String("foo1", "", "")
-	c.MarkFlagRequired("foo1")
+	assertNoErr(t, c.MarkFlagRequired("foo1"))
 	c.Flags().String("foo2", "", "")
-	c.MarkFlagRequired("foo2")
+	assertNoErr(t, c.MarkFlagRequired("foo2"))
 	c.Flags().String("bar", "", "")
 
 	expected := fmt.Sprintf("required flag(s) %q, %q not set", "foo1", "foo2")
@@ -764,16 +755,16 @@ func TestRequiredFlags(t *testing.T) {
 func TestPersistentRequiredFlags(t *testing.T) {
 	parent := &Command{Use: "parent", Run: emptyRun}
 	parent.PersistentFlags().String("foo1", "", "")
-	parent.MarkPersistentFlagRequired("foo1")
+	assertNoErr(t, parent.MarkPersistentFlagRequired("foo1"))
 	parent.PersistentFlags().String("foo2", "", "")
-	parent.MarkPersistentFlagRequired("foo2")
+	assertNoErr(t, parent.MarkPersistentFlagRequired("foo2"))
 	parent.Flags().String("foo3", "", "")
 
 	child := &Command{Use: "child", Run: emptyRun}
 	child.Flags().String("bar1", "", "")
-	child.MarkFlagRequired("bar1")
+	assertNoErr(t, child.MarkFlagRequired("bar1"))
 	child.Flags().String("bar2", "", "")
-	child.MarkFlagRequired("bar2")
+	assertNoErr(t, child.MarkFlagRequired("bar2"))
 	child.Flags().String("bar3", "", "")
 
 	parent.AddCommand(child)
@@ -793,7 +784,7 @@ func TestPersistentRequiredFlagsWithDisableFlagParsing(t *testing.T) {
 	parent := &Command{Use: "parent", Run: emptyRun}
 	parent.PersistentFlags().Bool("foo", false, "")
 	flag := parent.PersistentFlags().Lookup("foo")
-	parent.MarkPersistentFlagRequired("foo")
+	assertNoErr(t, parent.MarkPersistentFlagRequired("foo"))
 
 	child := &Command{Use: "child", Run: emptyRun}
 	child.DisableFlagParsing = true
@@ -1299,20 +1290,19 @@ func TestHooks(t *testing.T) {
 		t.Errorf("Unexpected error: %v", err)
 	}
 
-	if persPreArgs != "one two" {
-		t.Errorf("Expected persPreArgs %q, got %q", "one two", persPreArgs)
-	}
-	if preArgs != "one two" {
-		t.Errorf("Expected preArgs %q, got %q", "one two", preArgs)
-	}
-	if runArgs != "one two" {
-		t.Errorf("Expected runArgs %q, got %q", "one two", runArgs)
-	}
-	if postArgs != "one two" {
-		t.Errorf("Expected postArgs %q, got %q", "one two", postArgs)
-	}
-	if persPostArgs != "one two" {
-		t.Errorf("Expected persPostArgs %q, got %q", "one two", persPostArgs)
+	for _, v := range []struct {
+		name string
+		got  string
+	}{
+		{"persPreArgs", persPreArgs},
+		{"preArgs", preArgs},
+		{"runArgs", runArgs},
+		{"postArgs", postArgs},
+		{"persPostArgs", persPostArgs},
+	} {
+		if v.got != onetwo {
+			t.Errorf("Expected %s %q, got %q", v.name, onetwo, v.got)
+		}
 	}
 }
 
@@ -1380,44 +1370,42 @@ func TestPersistentHooks(t *testing.T) {
 		t.Errorf("Unexpected error: %v", err)
 	}
 
-	// TODO: currently PersistenPreRun* defined in parent does not
-	// run if the matchin child subcommand has PersistenPreRun.
-	// If the behavior changes (https://github.com/spf13/cobra/issues/252)
-	// this test must be fixed.
-	if parentPersPreArgs != "" {
-		t.Errorf("Expected blank parentPersPreArgs, got %q", parentPersPreArgs)
-	}
-	if parentPreArgs != "" {
-		t.Errorf("Expected blank parentPreArgs, got %q", parentPreArgs)
-	}
-	if parentRunArgs != "" {
-		t.Errorf("Expected blank parentRunArgs, got %q", parentRunArgs)
-	}
-	if parentPostArgs != "" {
-		t.Errorf("Expected blank parentPostArgs, got %q", parentPostArgs)
-	}
-	// TODO: currently PersistenPostRun* defined in parent does not
-	// run if the matchin child subcommand has PersistenPostRun.
-	// If the behavior changes (https://github.com/spf13/cobra/issues/252)
-	// this test must be fixed.
-	if parentPersPostArgs != "" {
-		t.Errorf("Expected blank parentPersPostArgs, got %q", parentPersPostArgs)
+	for _, v := range []struct {
+		name string
+		got  string
+	}{
+		// TODO: currently PersistenPreRun* defined in parent does not
+		// run if the matchin child subcommand has PersistenPreRun.
+		// If the behavior changes (https://github.com/spf13/cobra/issues/252)
+		// this test must be fixed.
+		{"parentPersPreArgs", parentPersPreArgs},
+		{"parentPreArgs", parentPreArgs},
+		{"parentRunArgs", parentRunArgs},
+		{"parentPostArgs", parentPostArgs},
+		// TODO: currently PersistenPostRun* defined in parent does not
+		// run if the matchin child subcommand has PersistenPostRun.
+		// If the behavior changes (https://github.com/spf13/cobra/issues/252)
+		// this test must be fixed.
+		{"parentPersPostArgs", parentPersPostArgs},
+	} {
+		if v.got != "" {
+			t.Errorf("Expected blank %s, got %q", v.name, v.got)
+		}
 	}
 
-	if childPersPreArgs != "one two" {
-		t.Errorf("Expected childPersPreArgs %q, got %q", "one two", childPersPreArgs)
-	}
-	if childPreArgs != "one two" {
-		t.Errorf("Expected childPreArgs %q, got %q", "one two", childPreArgs)
-	}
-	if childRunArgs != "one two" {
-		t.Errorf("Expected childRunArgs %q, got %q", "one two", childRunArgs)
-	}
-	if childPostArgs != "one two" {
-		t.Errorf("Expected childPostArgs %q, got %q", "one two", childPostArgs)
-	}
-	if childPersPostArgs != "one two" {
-		t.Errorf("Expected childPersPostArgs %q, got %q", "one two", childPersPostArgs)
+	for _, v := range []struct {
+		name string
+		got  string
+	}{
+		{"childPersPreArgs", childPersPreArgs},
+		{"childPreArgs", childPreArgs},
+		{"childRunArgs", childRunArgs},
+		{"childPostArgs", childPostArgs},
+		{"childPersPostArgs", childPersPostArgs},
+	} {
+		if v.got != onetwo {
+			t.Errorf("Expected %s %q, got %q", v.name, onetwo, v.got)
+		}
 	}
 }
 
@@ -1741,7 +1729,7 @@ func TestMergeCommandLineToFlags(t *testing.T) {
 func TestUseDeprecatedFlags(t *testing.T) {
 	c := &Command{Use: "c", Run: emptyRun}
 	c.Flags().BoolP("deprecated", "d", false, "deprecated flag")
-	c.Flags().MarkDeprecated("deprecated", "This flag is deprecated")
+	assertNoErr(t, c.Flags().MarkDeprecated("deprecated", "This flag is deprecated"))
 
 	output, err := executeCommand(c, "c", "-d")
 	if err != nil {
@@ -1868,7 +1856,6 @@ type calledAsTestcase struct {
 	call string
 	want string
 	epm  bool
-	tc   bool
 }
 
 func (tc *calledAsTestcase) test(t *testing.T) {
@@ -1890,7 +1877,7 @@ func (tc *calledAsTestcase) test(t *testing.T) {
 	parent.SetOut(output)
 	parent.SetErr(output)
 
-	parent.Execute()
+	_ = parent.Execute()
 
 	if called == nil {
 		if tc.call != "" {
@@ -1908,18 +1895,18 @@ func (tc *calledAsTestcase) test(t *testing.T) {
 
 func TestCalledAs(t *testing.T) {
 	tests := map[string]calledAsTestcase{
-		"find/no-args":            {nil, "parent", "parent", false, false},
-		"find/real-name":          {[]string{"child1"}, "child1", "child1", false, false},
-		"find/full-alias":         {[]string{"that"}, "child2", "that", false, false},
-		"find/part-no-prefix":     {[]string{"thi"}, "", "", false, false},
-		"find/part-alias":         {[]string{"thi"}, "child1", "this", true, false},
-		"find/conflict":           {[]string{"th"}, "", "", true, false},
-		"traverse/no-args":        {nil, "parent", "parent", false, true},
-		"traverse/real-name":      {[]string{"child1"}, "child1", "child1", false, true},
-		"traverse/full-alias":     {[]string{"that"}, "child2", "that", false, true},
-		"traverse/part-no-prefix": {[]string{"thi"}, "", "", false, true},
-		"traverse/part-alias":     {[]string{"thi"}, "child1", "this", true, true},
-		"traverse/conflict":       {[]string{"th"}, "", "", true, true},
+		"find/no-args":            {nil, "parent", "parent", false},
+		"find/real-name":          {[]string{"child1"}, "child1", "child1", false},
+		"find/full-alias":         {[]string{"that"}, "child2", "that", false},
+		"find/part-no-prefix":     {[]string{"thi"}, "", "", false},
+		"find/part-alias":         {[]string{"thi"}, "child1", "this", true},
+		"find/conflict":           {[]string{"th"}, "", "", true},
+		"traverse/no-args":        {nil, "parent", "parent", false},
+		"traverse/real-name":      {[]string{"child1"}, "child1", "child1", false},
+		"traverse/full-alias":     {[]string{"that"}, "child2", "that", false},
+		"traverse/part-no-prefix": {[]string{"thi"}, "", "", false},
+		"traverse/part-alias":     {[]string{"thi"}, "child1", "this", true},
+		"traverse/conflict":       {[]string{"th"}, "", "", true},
 	}
 
 	for name, tc := range tests {
diff --git a/custom_completions.go b/custom_completions.go
index f9e88e081..fa060c147 100644
--- a/custom_completions.go
+++ b/custom_completions.go
@@ -527,13 +527,13 @@ func CompDebug(msg string, printToStdErr bool) {
 			os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
 		if err == nil {
 			defer f.Close()
-			f.WriteString(msg)
+			WriteStringAndCheck(f, msg)
 		}
 	}
 
 	if printToStdErr {
 		// Must print to stderr for this not to be read by the completion script.
-		fmt.Fprintf(os.Stderr, msg)
+		fmt.Fprint(os.Stderr, msg)
 	}
 }
 
diff --git a/custom_completions_test.go b/custom_completions_test.go
index 14ec5a9eb..ede809ed4 100644
--- a/custom_completions_test.go
+++ b/custom_completions_test.go
@@ -780,17 +780,17 @@ func TestRequiredFlagNameCompletionInGo(t *testing.T) {
 	rootCmd.AddCommand(childCmd)
 
 	rootCmd.Flags().IntP("requiredFlag", "r", -1, "required flag")
-	rootCmd.MarkFlagRequired("requiredFlag")
+	assertNoErr(t, rootCmd.MarkFlagRequired("requiredFlag"))
 	requiredFlag := rootCmd.Flags().Lookup("requiredFlag")
 
 	rootCmd.PersistentFlags().IntP("requiredPersistent", "p", -1, "required persistent")
-	rootCmd.MarkPersistentFlagRequired("requiredPersistent")
+	assertNoErr(t, rootCmd.MarkPersistentFlagRequired("requiredPersistent"))
 	requiredPersistent := rootCmd.PersistentFlags().Lookup("requiredPersistent")
 
 	rootCmd.Flags().StringP("release", "R", "", "Release name")
 
 	childCmd.Flags().BoolP("subRequired", "s", false, "sub required flag")
-	childCmd.MarkFlagRequired("subRequired")
+	assertNoErr(t, childCmd.MarkFlagRequired("subRequired"))
 	childCmd.Flags().BoolP("subNotRequired", "n", false, "sub not required flag")
 
 	// Test that a required flag is suggested even without the - prefix
@@ -964,19 +964,19 @@ func TestFlagFileExtFilterCompletionInGo(t *testing.T) {
 
 	// No extensions.  Should be ignored.
 	rootCmd.Flags().StringP("file", "f", "", "file flag")
-	rootCmd.MarkFlagFilename("file")
+	assertNoErr(t, rootCmd.MarkFlagFilename("file"))
 
 	// Single extension
 	rootCmd.Flags().StringP("log", "l", "", "log flag")
-	rootCmd.MarkFlagFilename("log", "log")
+	assertNoErr(t, rootCmd.MarkFlagFilename("log", "log"))
 
 	// Multiple extensions
 	rootCmd.Flags().StringP("yaml", "y", "", "yaml flag")
-	rootCmd.MarkFlagFilename("yaml", "yaml", "yml")
+	assertNoErr(t, rootCmd.MarkFlagFilename("yaml", "yaml", "yml"))
 
 	// Directly using annotation
 	rootCmd.Flags().StringP("text", "t", "", "text flag")
-	rootCmd.Flags().SetAnnotation("text", BashCompFilenameExt, []string{"txt"})
+	assertNoErr(t, rootCmd.Flags().SetAnnotation("text", BashCompFilenameExt, []string{"txt"}))
 
 	// Test that the completion logic returns the proper info for the completion
 	// script to handle the file filtering
@@ -1086,15 +1086,15 @@ func TestFlagDirFilterCompletionInGo(t *testing.T) {
 
 	// Filter directories
 	rootCmd.Flags().StringP("dir", "d", "", "dir flag")
-	rootCmd.MarkFlagDirname("dir")
+	assertNoErr(t, rootCmd.MarkFlagDirname("dir"))
 
 	// Filter directories within a directory
 	rootCmd.Flags().StringP("subdir", "s", "", "subdir")
-	rootCmd.Flags().SetAnnotation("subdir", BashCompSubdirsInDir, []string{"themes"})
+	assertNoErr(t, rootCmd.Flags().SetAnnotation("subdir", BashCompSubdirsInDir, []string{"themes"}))
 
 	// Multiple directory specification get ignored
 	rootCmd.Flags().StringP("manydir", "m", "", "manydir")
-	rootCmd.Flags().SetAnnotation("manydir", BashCompSubdirsInDir, []string{"themes", "colors"})
+	assertNoErr(t, rootCmd.Flags().SetAnnotation("manydir", BashCompSubdirsInDir, []string{"themes", "colors"}))
 
 	// Test that the completion logic returns the proper info for the completion
 	// script to handle the directory filtering
@@ -1430,7 +1430,7 @@ func TestValidArgsFuncInBashScript(t *testing.T) {
 	rootCmd.AddCommand(child)
 
 	buf := new(bytes.Buffer)
-	rootCmd.GenBashCompletion(buf)
+	assertNoErr(t, rootCmd.GenBashCompletion(buf))
 	output := buf.String()
 
 	check(t, output, "has_completion_function=1")
@@ -1445,7 +1445,7 @@ func TestNoValidArgsFuncInBashScript(t *testing.T) {
 	rootCmd.AddCommand(child)
 
 	buf := new(bytes.Buffer)
-	rootCmd.GenBashCompletion(buf)
+	assertNoErr(t, rootCmd.GenBashCompletion(buf))
 	output := buf.String()
 
 	checkOmit(t, output, "has_completion_function=1")
@@ -1461,7 +1461,7 @@ func TestCompleteCmdInBashScript(t *testing.T) {
 	rootCmd.AddCommand(child)
 
 	buf := new(bytes.Buffer)
-	rootCmd.GenBashCompletion(buf)
+	assertNoErr(t, rootCmd.GenBashCompletion(buf))
 	output := buf.String()
 
 	check(t, output, ShellCompNoDescRequestCmd)
@@ -1477,7 +1477,7 @@ func TestCompleteNoDesCmdInZshScript(t *testing.T) {
 	rootCmd.AddCommand(child)
 
 	buf := new(bytes.Buffer)
-	rootCmd.GenZshCompletionNoDesc(buf)
+	assertNoErr(t, rootCmd.GenZshCompletionNoDesc(buf))
 	output := buf.String()
 
 	check(t, output, ShellCompNoDescRequestCmd)
@@ -1493,7 +1493,7 @@ func TestCompleteCmdInZshScript(t *testing.T) {
 	rootCmd.AddCommand(child)
 
 	buf := new(bytes.Buffer)
-	rootCmd.GenZshCompletion(buf)
+	assertNoErr(t, rootCmd.GenZshCompletion(buf))
 	output := buf.String()
 
 	check(t, output, ShellCompRequestCmd)
@@ -1506,7 +1506,7 @@ func TestFlagCompletionInGo(t *testing.T) {
 		Run: emptyRun,
 	}
 	rootCmd.Flags().IntP("introot", "i", -1, "help message for flag introot")
-	rootCmd.RegisterFlagCompletionFunc("introot", func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective) {
+	assertNoErr(t, rootCmd.RegisterFlagCompletionFunc("introot", func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective) {
 		completions := []string{}
 		for _, comp := range []string{"1\tThe first", "2\tThe second", "10\tThe tenth"} {
 			if strings.HasPrefix(comp, toComplete) {
@@ -1514,9 +1514,9 @@ func TestFlagCompletionInGo(t *testing.T) {
 			}
 		}
 		return completions, ShellCompDirectiveDefault
-	})
+	}))
 	rootCmd.Flags().String("filename", "", "Enter a filename")
-	rootCmd.RegisterFlagCompletionFunc("filename", func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective) {
+	assertNoErr(t, rootCmd.RegisterFlagCompletionFunc("filename", func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective) {
 		completions := []string{}
 		for _, comp := range []string{"file.yaml\tYAML format", "myfile.json\tJSON format", "file.xml\tXML format"} {
 			if strings.HasPrefix(comp, toComplete) {
@@ -1524,7 +1524,7 @@ func TestFlagCompletionInGo(t *testing.T) {
 			}
 		}
 		return completions, ShellCompDirectiveNoSpace | ShellCompDirectiveNoFileComp
-	})
+	}))
 
 	// Test completing an empty string
 	output, err := executeCommand(rootCmd, ShellCompNoDescRequestCmd, "--introot", "")
@@ -1703,7 +1703,7 @@ func TestFlagCompletionInGoWithDesc(t *testing.T) {
 		Run: emptyRun,
 	}
 	rootCmd.Flags().IntP("introot", "i", -1, "help message for flag introot")
-	rootCmd.RegisterFlagCompletionFunc("introot", func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective) {
+	assertNoErr(t, rootCmd.RegisterFlagCompletionFunc("introot", func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective) {
 		completions := []string{}
 		for _, comp := range []string{"1\tThe first", "2\tThe second", "10\tThe tenth"} {
 			if strings.HasPrefix(comp, toComplete) {
@@ -1711,9 +1711,9 @@ func TestFlagCompletionInGoWithDesc(t *testing.T) {
 			}
 		}
 		return completions, ShellCompDirectiveDefault
-	})
+	}))
 	rootCmd.Flags().String("filename", "", "Enter a filename")
-	rootCmd.RegisterFlagCompletionFunc("filename", func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective) {
+	assertNoErr(t, rootCmd.RegisterFlagCompletionFunc("filename", func(cmd *Command, args []string, toComplete string) ([]string, ShellCompDirective) {
 		completions := []string{}
 		for _, comp := range []string{"file.yaml\tYAML format", "myfile.json\tJSON format", "file.xml\tXML format"} {
 			if strings.HasPrefix(comp, toComplete) {
@@ -1721,7 +1721,7 @@ func TestFlagCompletionInGoWithDesc(t *testing.T) {
 			}
 		}
 		return completions, ShellCompDirectiveNoSpace | ShellCompDirectiveNoFileComp
-	})
+	}))
 
 	// Test completing an empty string
 	output, err := executeCommand(rootCmd, ShellCompRequestCmd, "--introot", "")
diff --git a/doc/man_docs.go b/doc/man_docs.go
index b67ac1f1c..916e36144 100644
--- a/doc/man_docs.go
+++ b/doc/man_docs.go
@@ -139,23 +139,23 @@ func fillHeader(header *GenManHeader, name string, disableAutoGen bool) error {
 	return nil
 }
 
-func manPreamble(buf *bytes.Buffer, header *GenManHeader, cmd *cobra.Command, dashedName string) {
+func manPreamble(buf io.StringWriter, header *GenManHeader, cmd *cobra.Command, dashedName string) {
 	description := cmd.Long
 	if len(description) == 0 {
 		description = cmd.Short
 	}
 
-	buf.WriteString(fmt.Sprintf(`%% "%s" "%s" "%s" "%s" "%s"
+	cobra.WriteStringAndCheck(buf, fmt.Sprintf(`%% "%s" "%s" "%s" "%s" "%s"
 # NAME
 `, header.Title, header.Section, header.date, header.Source, header.Manual))
-	buf.WriteString(fmt.Sprintf("%s \\- %s\n\n", dashedName, cmd.Short))
-	buf.WriteString("# SYNOPSIS\n")
-	buf.WriteString(fmt.Sprintf("**%s**\n\n", cmd.UseLine()))
-	buf.WriteString("# DESCRIPTION\n")
-	buf.WriteString(description + "\n\n")
+	cobra.WriteStringAndCheck(buf, fmt.Sprintf("%s \\- %s\n\n", dashedName, cmd.Short))
+	cobra.WriteStringAndCheck(buf, "# SYNOPSIS\n")
+	cobra.WriteStringAndCheck(buf, fmt.Sprintf("**%s**\n\n", cmd.UseLine()))
+	cobra.WriteStringAndCheck(buf, "# DESCRIPTION\n")
+	cobra.WriteStringAndCheck(buf, description+"\n\n")
 }
 
-func manPrintFlags(buf *bytes.Buffer, flags *pflag.FlagSet) {
+func manPrintFlags(buf io.StringWriter, flags *pflag.FlagSet) {
 	flags.VisitAll(func(flag *pflag.Flag) {
 		if len(flag.Deprecated) > 0 || flag.Hidden {
 			return
@@ -179,22 +179,22 @@ func manPrintFlags(buf *bytes.Buffer, flags *pflag.FlagSet) {
 			format += "]"
 		}
 		format += "\n\t%s\n\n"
-		buf.WriteString(fmt.Sprintf(format, flag.DefValue, flag.Usage))
+		cobra.WriteStringAndCheck(buf, fmt.Sprintf(format, flag.DefValue, flag.Usage))
 	})
 }
 
-func manPrintOptions(buf *bytes.Buffer, command *cobra.Command) {
+func manPrintOptions(buf io.StringWriter, command *cobra.Command) {
 	flags := command.NonInheritedFlags()
 	if flags.HasAvailableFlags() {
-		buf.WriteString("# OPTIONS\n")
+		cobra.WriteStringAndCheck(buf, "# OPTIONS\n")
 		manPrintFlags(buf, flags)
-		buf.WriteString("\n")
+		cobra.WriteStringAndCheck(buf, "\n")
 	}
 	flags = command.InheritedFlags()
 	if flags.HasAvailableFlags() {
-		buf.WriteString("# OPTIONS INHERITED FROM PARENT COMMANDS\n")
+		cobra.WriteStringAndCheck(buf, "# OPTIONS INHERITED FROM PARENT COMMANDS\n")
 		manPrintFlags(buf, flags)
-		buf.WriteString("\n")
+		cobra.WriteStringAndCheck(buf, "\n")
 	}
 }
 
diff --git a/doc/man_docs_test.go b/doc/man_docs_test.go
index ee9b87535..aa3f5f2a1 100644
--- a/doc/man_docs_test.go
+++ b/doc/man_docs_test.go
@@ -13,6 +13,12 @@ import (
 	"github.com/spf13/cobra"
 )
 
+func assertNoErr(t *testing.T, e error) {
+	if e != nil {
+		t.Error(e)
+	}
+}
+
 func translate(in string) string {
 	return strings.Replace(in, "-", "\\-", -1)
 }
@@ -133,7 +139,7 @@ func TestGenManSeeAlso(t *testing.T) {
 func TestManPrintFlagsHidesShortDeperecated(t *testing.T) {
 	c := &cobra.Command{}
 	c.Flags().StringP("foo", "f", "default", "Foo flag")
-	c.Flags().MarkShorthandDeprecated("foo", "don't use it no more")
+	assertNoErr(t, c.Flags().MarkShorthandDeprecated("foo", "don't use it no more"))
 
 	buf := new(bytes.Buffer)
 	manPrintFlags(buf, c.Flags())
diff --git a/doc/man_examples_test.go b/doc/man_examples_test.go
index db6604268..e20a34c38 100644
--- a/doc/man_examples_test.go
+++ b/doc/man_examples_test.go
@@ -17,7 +17,7 @@ func ExampleGenManTree() {
 		Title:   "MINE",
 		Section: "3",
 	}
-	doc.GenManTree(cmd, header, "/tmp")
+	cobra.CheckErr(doc.GenManTree(cmd, header, "/tmp"))
 }
 
 func ExampleGenMan() {
@@ -30,6 +30,6 @@ func ExampleGenMan() {
 		Section: "3",
 	}
 	out := new(bytes.Buffer)
-	doc.GenMan(cmd, header, out)
+	cobra.CheckErr(doc.GenMan(cmd, header, out))
 	fmt.Print(out.String())
 }
diff --git a/fish_completions.go b/fish_completions.go
index eaae9bca8..3e112347d 100644
--- a/fish_completions.go
+++ b/fish_completions.go
@@ -8,7 +8,7 @@ import (
 	"strings"
 )
 
-func genFishComp(buf *bytes.Buffer, name string, includeDesc bool) {
+func genFishComp(buf io.StringWriter, name string, includeDesc bool) {
 	// Variables should not contain a '-' or ':' character
 	nameForVar := name
 	nameForVar = strings.Replace(nameForVar, "-", "_", -1)
@@ -18,8 +18,8 @@ func genFishComp(buf *bytes.Buffer, name string, includeDesc bool) {
 	if !includeDesc {
 		compCmd = ShellCompNoDescRequestCmd
 	}
-	buf.WriteString(fmt.Sprintf("# fish completion for %-36s -*- shell-script -*-\n", name))
-	buf.WriteString(fmt.Sprintf(`
+	WriteStringAndCheck(buf, fmt.Sprintf("# fish completion for %-36s -*- shell-script -*-\n", name))
+	WriteStringAndCheck(buf, fmt.Sprintf(`
 function __%[1]s_debug
     set file "$BASH_COMP_DEBUG_FILE"
     if test -n "$file"
diff --git a/fish_completions_test.go b/fish_completions_test.go
index 532b6055a..a3171e481 100644
--- a/fish_completions_test.go
+++ b/fish_completions_test.go
@@ -15,7 +15,7 @@ func TestCompleteNoDesCmdInFishScript(t *testing.T) {
 	rootCmd.AddCommand(child)
 
 	buf := new(bytes.Buffer)
-	rootCmd.GenFishCompletion(buf, false)
+	assertNoErr(t, rootCmd.GenFishCompletion(buf, false))
 	output := buf.String()
 
 	check(t, output, ShellCompNoDescRequestCmd)
@@ -31,7 +31,7 @@ func TestCompleteCmdInFishScript(t *testing.T) {
 	rootCmd.AddCommand(child)
 
 	buf := new(bytes.Buffer)
-	rootCmd.GenFishCompletion(buf, true)
+	assertNoErr(t, rootCmd.GenFishCompletion(buf, true))
 	output := buf.String()
 
 	check(t, output, ShellCompRequestCmd)
@@ -41,7 +41,7 @@ func TestCompleteCmdInFishScript(t *testing.T) {
 func TestProgWithDash(t *testing.T) {
 	rootCmd := &Command{Use: "root-dash", Args: NoArgs, Run: emptyRun}
 	buf := new(bytes.Buffer)
-	rootCmd.GenFishCompletion(buf, false)
+	assertNoErr(t, rootCmd.GenFishCompletion(buf, false))
 	output := buf.String()
 
 	// Functions name should have replace the '-'
@@ -56,7 +56,7 @@ func TestProgWithDash(t *testing.T) {
 func TestProgWithColon(t *testing.T) {
 	rootCmd := &Command{Use: "root:colon", Args: NoArgs, Run: emptyRun}
 	buf := new(bytes.Buffer)
-	rootCmd.GenFishCompletion(buf, false)
+	assertNoErr(t, rootCmd.GenFishCompletion(buf, false))
 	output := buf.String()
 
 	// Functions name should have replace the ':'
diff --git a/powershell_completions.go b/powershell_completions.go
index 48022ea5b..6267f694f 100644
--- a/powershell_completions.go
+++ b/powershell_completions.go
@@ -10,12 +10,12 @@ import (
 	"os"
 )
 
-func genPowerShellComp(buf *bytes.Buffer, name string, includeDesc bool) {
+func genPowerShellComp(buf io.StringWriter, name string, includeDesc bool) {
 	compCmd := ShellCompRequestCmd
 	if !includeDesc {
 		compCmd = ShellCompNoDescRequestCmd
 	}
-	buf.WriteString(fmt.Sprintf(`# powershell completion for %-36[1]s -*- shell-script -*-
+	WriteStringAndCheck(buf, fmt.Sprintf(`# powershell completion for %-36[1]s -*- shell-script -*-
 
 function __%[1]s_debug {
     if ($env:BASH_COMP_DEBUG_FILE) {
@@ -46,12 +46,12 @@ Register-ArgumentCompleter -CommandName '%[1]s' -ScriptBlock {
     # We need to trigger completion from the $CursorPosition location, so we need
     # to truncate the command-line ($Command) up to the $CursorPosition location.
     # Make sure the $Command is longer then the $CursorPosition before we truncate.
-    # This happens because the $Command does not include the last space.    
+    # This happens because the $Command does not include the last space.
     if ($Command.Length -gt $CursorPosition) {
         $Command=$Command.Substring(0,$CursorPosition)
     }
 	__%[1]s_debug "Truncated command: $Command"
-	
+
     $ShellCompDirectiveError=%[3]d
     $ShellCompDirectiveNoSpace=%[4]d
     $ShellCompDirectiveNoFileComp=%[5]d
@@ -64,7 +64,7 @@ Register-ArgumentCompleter -CommandName '%[1]s' -ScriptBlock {
     $RequestComp="$Program %[2]s $Arguments"
     __%[1]s_debug "RequestComp: $RequestComp"
 
-    # we cannot use $WordToComplete because it 
+    # we cannot use $WordToComplete because it
     # has the wrong values if the cursor was moved
     # so use the last argument
     if ($WordToComplete -ne "" ) {
@@ -102,7 +102,7 @@ Register-ArgumentCompleter -CommandName '%[1]s' -ScriptBlock {
         $Directive = 0
     }
     __%[1]s_debug "The completion directive is: $Directive"
-    
+
     # remove directive (last element) from out
     $Out = $Out | Where-Object { $_ -ne $Out[-1] }
     __%[1]s_debug "The completions are: $Out"
@@ -142,18 +142,18 @@ Register-ArgumentCompleter -CommandName '%[1]s' -ScriptBlock {
 
     if (($Directive -band $ShellCompDirectiveNoFileComp) -ne 0 ) {
         __%[1]s_debug "ShellCompDirectiveNoFileComp is called"
-        
+
         if ($Values.Length -eq 0) {
-            # Just print an empty string here so the 
+            # Just print an empty string here so the
             # shell does not start to complete paths.
-            # We cannot use CompletionResult here because 
+            # We cannot use CompletionResult here because
             # it does not accept an empty string as argument.
             ""
             return
         }
     }
 
-    if ((($Directive -band $ShellCompDirectiveFilterFileExt) -ne 0 ) -or 
+    if ((($Directive -band $ShellCompDirectiveFilterFileExt) -ne 0 ) -or
        (($Directive -band $ShellCompDirectiveFilterDirs) -ne 0 ))  {
         __%[1]s_debug "ShellCompDirectiveFilterFileExt ShellCompDirectiveFilterDirs are not supported"
 
@@ -170,7 +170,7 @@ Register-ArgumentCompleter -CommandName '%[1]s' -ScriptBlock {
             __%[1]s_debug "Join the equal sign flag back to the completion value"
             $_.Name = $Flag + "=" + $_.Name
         }
-    } 
+    }
 
     # Get the current mode
     $Mode = (Get-PSReadLineKeyHandler | Where-Object {$_.Key -eq "Tab" }).Function
@@ -224,14 +224,14 @@ Register-ArgumentCompleter -CommandName '%[1]s' -ScriptBlock {
             # zsh like
             "MenuComplete" {
                 # insert space after value
-                # MenuComplete will automatically show the ToolTip of 
+                # MenuComplete will automatically show the ToolTip of
                 # the highlighted value at the bottom of the suggestions.
                 [System.Management.Automation.CompletionResult]::new($($comp.Name | __%[1]s_escapeStringWithSpecialChars) + $Space, "$($comp.Name)", 'ParameterValue', "$($comp.Description)")
             }
 
             # TabCompleteNext and in case we get something unknown
             Default {
-                # Like MenuComplete but we don't want to add a space here because 
+                # Like MenuComplete but we don't want to add a space here because
                 # the user need to press space anyway to get the completion.
                 # Description will not be shown because thats not possible with TabCompleteNext
                 [System.Management.Automation.CompletionResult]::new($($comp.Name | __%[1]s_escapeStringWithSpecialChars), "$($comp.Name)", 'ParameterValue', "$($comp.Description)")
diff --git a/shell_completions.md b/shell_completions.md
index 511b2f3ca..d557d8a67 100644
--- a/shell_completions.md
+++ b/shell_completions.md
@@ -99,8 +99,7 @@ cmd := &cobra.Command{
 	Long:    get_long,
 	Example: get_example,
 	Run: func(cmd *cobra.Command, args []string) {
-		err := RunGet(f, out, cmd, args)
-		util.CheckErr(err)
+		cobra.CheckErr(RunGet(f, out, cmd, args))
 	},
 	ValidArgs: validArgs,
 }
@@ -132,7 +131,7 @@ the completion algorithm if entered manually, e.g. in:
 
 ```bash
 $ kubectl get rc [tab][tab]
-backend        frontend       database 
+backend        frontend       database
 ```
 
 Note that without declaring `rc` as an alias, the completion algorithm would not know to show the list of
@@ -254,7 +253,7 @@ and you'll get something like
 
 ```bash
 $ kubectl exec [tab][tab]
--c            --container=  -p            --pod=  
+-c            --container=  -p            --pod=
 ```
 
 ### Specify dynamic flag completion
diff --git a/zsh_completions.go b/zsh_completions.go
index 92a70394a..2e840285f 100644
--- a/zsh_completions.go
+++ b/zsh_completions.go
@@ -70,12 +70,12 @@ func (c *Command) genZshCompletion(w io.Writer, includeDesc bool) error {
 	return err
 }
 
-func genZshComp(buf *bytes.Buffer, name string, includeDesc bool) {
+func genZshComp(buf io.StringWriter, name string, includeDesc bool) {
 	compCmd := ShellCompRequestCmd
 	if !includeDesc {
 		compCmd = ShellCompNoDescRequestCmd
 	}
-	buf.WriteString(fmt.Sprintf(`#compdef _%[1]s %[1]s
+	WriteStringAndCheck(buf, fmt.Sprintf(`#compdef _%[1]s %[1]s
 
 # zsh completion for %-36[1]s -*- shell-script -*-