fix(ec2): InitCommand.shellCommand() renders an argv command instead (

#10691)

`InitCommand.shellCommand('abc xyz')` renders to `['abc xyz']` which actually
represents an `argv` command of one element, which is treated
differently. For example, spaces in it are not parsed, which would
be expected for a shell command.

The correct rendering for a shell command is a plain string in the
`command` property.

Fixes #10684.


----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-ec2/lib/cfn-init-elements.ts

@@ -211,7 +211,7 @@ export class InitCommand extends InitElement {
    * need to be preceded by a `\` if you want to treat them as part of a filename.
    */
   public static shellCommand(shellCommand: string, options: InitCommandOptions = {}): InitCommand {
-    return new InitCommand([shellCommand], options);
+    return new InitCommand(shellCommand, options);
   }
 
   /**
@@ -228,7 +228,7 @@ export class InitCommand extends InitElement {
 
   public readonly elementType = InitElementType.COMMAND.toString();
 
-  private constructor(private readonly command: string[], private readonly options: InitCommandOptions) {
+  private constructor(private readonly command: string[] | string, private readonly options: InitCommandOptions) {
     super();
   }
 

packages/@aws-cdk/aws-ec2/test/cfn-init-element.test.ts

@@ -44,7 +44,20 @@ describe('InitCommand', () => {
 
     // THEN
     expect(rendered).toEqual({
-      '000': { command: ['/bin/sh'] },
+      '000': { command: '/bin/sh' },
+    });
+  });
+
+  test('shell command is rendered as string', () => {
+    // GIVEN
+    const command = ec2.InitCommand.shellCommand('/bin/sh -c "echo hello"');
+
+    // WHEN
+    const rendered = getElementConfig(command, InitPlatform.LINUX);
+
+    // THEN
+    expect(rendered).toEqual({
+      '000': { command: '/bin/sh -c "echo hello"' },
     });
   });
 
@@ -65,7 +78,7 @@ describe('InitCommand', () => {
     // THEN
     expect(rendered).toEqual({
       command_0: {
-        command: ['/bin/sh'],
+        command: '/bin/sh',
         env: { SECRETS_FILE: '/tmp/secrets' },
         cwd: '/home/myUser',
         test: 'test -d /home/myUser',