Have cmd/bash image actually use bash

- Base cmd/bash image on ubuntu, run specified args with "bash -c"
- Fail cmd/bash if extra args are passed -- these would have been ignored previously
- Fix examples for cmd/bash that passed extra args
- Update entrypoint image to be based on distroless (the default), since it doesn't actually need a shell
- Un-export unnecessarily exported types in entrypoint

Fixes #1445

.ko.yaml

@@ -1,6 +1,5 @@
 baseImageOverrides:
   github.com/tektoncd/pipeline/cmd/creds-init: gcr.io/tekton-nightly/github.com/tektoncd/pipeline/build-base:latest
   github.com/tektoncd/pipeline/cmd/git-init: gcr.io/tekton-nightly/github.com/tektoncd/pipeline/build-base:latest
-  github.com/tektoncd/pipeline/cmd/bash: busybox # image should have shell in $PATH
-  github.com/tektoncd/pipeline/cmd/entrypoint: busybox # image should have shell in $PATH
+  github.com/tektoncd/pipeline/cmd/bash: ubuntu # image should have bash in $PATH
   github.com/tektoncd/pipeline/cmd/gsutil: google/cloud-sdk:alpine # image should have gsutil in $PATH

cmd/bash/main.go

@@ -26,16 +26,19 @@ args: ['-args', 'ARGUMENTS_FOR_SHELL_COMMAND']
 For help, run `man sub-command`
 ```
 image: github.com/tektoncd/pipeline/cmd/bash
-args: ['-args', `man`,`mkdir`]
+args: ['-args', 'man mkdir']
 ```
 
 For example:
 Following example executes shell sub-command `mkdir`
 
 ```
 image: github.com/tektoncd/pipeline/cmd/bash
-args:  ['-args', 'mkdir', '-p', '/workspace/gcs-dir']
+args:  ['-args', 'mkdir -p /workspace/gcs-dir']
 ```
+
+Be sure not to pass multiple args to `-args`, only a single quoted string to
+execute. Passing further args will cause the image to raise an error.
 */
 
 package main
@@ -56,7 +59,11 @@ func main() {
 	flag.Parse()
 	logger, _ := logging.NewLogger("", "shell_command")
 	defer logger.Sync()
-	cmd := exec.Command("sh", "-c", *args)
+	if len(flag.Args()) > 0 {
+		logger.Fatalf("Extra args were provided, and would be ignored: %v", flag.Args())
+	}
+
+	cmd := exec.Command("bash", "-c", *args)
 	stdoutStderr, err := cmd.CombinedOutput()
 	if err != nil {
 		logger.Fatalf("Error executing command %q ; error %s; cmd_output %s", strings.Join(cmd.Args, " "), err.Error(), stdoutStderr)

cmd/entrypoint/main.go

@@ -46,9 +46,9 @@ func main() {
 		WaitFileContent: *waitFileContent,
 		PostFile:        *postFile,
 		Args:            flag.Args(),
-		Waiter:          &RealWaiter{},
-		Runner:          &RealRunner{},
-		PostWriter:      &RealPostWriter{},
+		Waiter:          &realWaiter{},
+		Runner:          &realRunner{},
+		PostWriter:      &realPostWriter{},
 	}
 	if err := e.Go(); err != nil {
 		switch t := err.(type) {

cmd/entrypoint/post_writer.go

@@ -7,12 +7,12 @@ import (
 	"github.com/tektoncd/pipeline/pkg/entrypoint"
 )
 
-// RealPostWriter actually writes files.
-type RealPostWriter struct{}
+// realPostWriter actually writes files.
+type realPostWriter struct{}
 
-var _ entrypoint.PostWriter = (*RealPostWriter)(nil)
+var _ entrypoint.PostWriter = (*realPostWriter)(nil)
 
-func (*RealPostWriter) Write(file string) {
+func (*realPostWriter) Write(file string) {
 	if file == "" {
 		return
 	}

cmd/entrypoint/runner.go

@@ -10,12 +10,12 @@ import (
 // TODO(jasonhall): Test that original exit code is propagated and that
 // stdout/stderr are collected -- needs e2e tests.
 
-// RealRunner actually runs commands.
-type RealRunner struct{}
+// realRunner actually runs commands.
+type realRunner struct{}
 
-var _ entrypoint.Runner = (*RealRunner)(nil)
+var _ entrypoint.Runner = (*realRunner)(nil)
 
-func (*RealRunner) Run(args ...string) error {
+func (*realRunner) Run(args ...string) error {
 	if len(args) == 0 {
 		return nil
 	}

cmd/entrypoint/waiter.go

@@ -8,10 +8,10 @@ import (
 	"golang.org/x/xerrors"
 )
 
-// RealWaiter actually waits for files, by polling.
-type RealWaiter struct{}
+// realWaiter actually waits for files, by polling.
+type realWaiter struct{}
 
-var _ entrypoint.Waiter = (*RealWaiter)(nil)
+var _ entrypoint.Waiter = (*realWaiter)(nil)
 
 // Wait watches a file and returns when either a) the file exists and, if
 // the expectContent argument is true, the file has non-zero size or b) there
@@ -22,7 +22,7 @@ var _ entrypoint.Waiter = (*RealWaiter)(nil)
 //
 // If a file of the same name with a ".err" extension exists then this Wait
 // will end with a skipError.
-func (*RealWaiter) Wait(file string, expectContent bool) error {
+func (*realWaiter) Wait(file string, expectContent bool) error {
 	if file == "" {
 		return nil
 	}

cmd/entrypoint/waiter_test.go

@@ -32,7 +32,7 @@ func TestRealWaiterWaitMissingFile(t *testing.T) {
 		t.Errorf("error creating temp file: %v", err)
 	}
 	os.Remove(tmp.Name())
-	rw := RealWaiter{}
+	rw := realWaiter{}
 	doneCh := make(chan struct{})
 	go func() {
 		err := rw.Wait(tmp.Name(), false)
@@ -55,7 +55,7 @@ func TestRealWaiterWaitWithFile(t *testing.T) {
 		t.Errorf("error creating temp file: %v", err)
 	}
 	defer os.Remove(tmp.Name())
-	rw := RealWaiter{}
+	rw := realWaiter{}
 	doneCh := make(chan struct{})
 	go func() {
 		err := rw.Wait(tmp.Name(), false)
@@ -78,7 +78,7 @@ func TestRealWaiterWaitMissingContent(t *testing.T) {
 		t.Errorf("error creating temp file: %v", err)
 	}
 	defer os.Remove(tmp.Name())
-	rw := RealWaiter{}
+	rw := realWaiter{}
 	doneCh := make(chan struct{})
 	go func() {
 		err := rw.Wait(tmp.Name(), true)
@@ -101,7 +101,7 @@ func TestRealWaiterWaitWithContent(t *testing.T) {
 		t.Errorf("error creating temp file: %v", err)
 	}
 	defer os.Remove(tmp.Name())
-	rw := RealWaiter{}
+	rw := realWaiter{}
 	doneCh := make(chan struct{})
 	go func() {
 		err := rw.Wait(tmp.Name(), true)