Add a flag for getting post meta as a single value or not

features/post-meta.feature

@@ -219,6 +219,39 @@ Feature: Manage post custom fields
       My\New\Meta
       """
 
+Scenario: List post meta with or without single flag
+    Given a WP install
+
+    When I run `wp post meta add 1 apple banana`
+    And I run `wp post meta add 1 apple banana`
+    Then STDOUT should not be empty
+
+    When I run `wp post meta get 1 apple`
+    Then STDOUT should be:
+      """
+      banana
+      """
+
+    When I run `wp post meta get 1 apple --single`
+    Then STDOUT should be:
+      """
+      banana
+      """
+
+    When I run `wp post meta get 1 apple --no-single`
+    Then STDOUT should be:
+      """
+      array (
+        0 => 'banana',
+        1 => 'banana',
+      )
+      """
+    When I run `wp post meta get 1 apple --no-single --format=json`
+    Then STDOUT should be:
+      """
+      ["banana","banana"]
+      """
+
   @pluck
   Scenario: Nested values can be retrieved.
     Given a WP install

src/WP_CLI/CommandWithMeta.php

@@ -142,6 +142,9 @@ function ( $a, $b ) use ( $orderby, $order ) {
 	 * <key>
 	 * : The name of the meta field to get.
 	 *
+	 * [--single]
+	 * : Whether to return a single value. This parameter has no effect if $key is not specified.
+	 *
 	 * [--format=<format>]
 	 * : Get value in a particular format.
 	 * ---
@@ -156,8 +159,9 @@ public function get( $args, $assoc_args ) {
 		list( $object_id, $meta_key ) = $args;
 
 		$object_id = $this->check_object_id( $object_id );
+		$single    = Utils\get_flag_value( $assoc_args, 'single', true );
 
-		$value = $this->get_metadata( $object_id, $meta_key, true );
+		$value = $this->get_metadata( $object_id, $meta_key, $single );
 
 		if ( '' === $value ) {
 			die( 1 );