wp-cli · Copilot · Feb 3, 2026 · Feb 3, 2026 · Feb 3, 2026 · Feb 3, 2026
@@ -1751,6 +1751,83 @@ Feature: WP-CLI Commands
       """
     And the return code should be 0
 
+  Scenario: Space-separated numeric arguments should be split on Windows
+    # This test simulates Windows PowerShell behavior using WP_CLI_TEST_IS_WINDOWS=1
+    # which activates the argument splitting logic on Unix-like test environments.
+    # The actual behavior on Windows systems will be identical.
+    Given an empty directory
+    And a custom-cmd.php file:
+      """
+      <?php
+      /**
+       * Test command for space-separated arguments
+       *
+       * <ids>...
+       * : One or more IDs
+       *
+       * @when before_wp_load
+       */
+      function test_ids_command( $args ) {
+        WP_CLI::log( 'Number of arguments: ' . count( $args ) );
+        foreach ( $args as $id ) {
+          WP_CLI::log( 'ID: ' . $id );
+        }
+      }
+      WP_CLI::add_command( 'test-ids', 'test_ids_command' );
+      """
+
+    # Test on Windows with space-separated IDs as a single argument
+    When I run `WP_CLI_TEST_IS_WINDOWS=1 wp --require=custom-cmd.php test-ids "123 456 789"`
+    Then STDOUT should contain:
+      """
+      Number of arguments: 3
+      """
+    And STDOUT should contain:
+      """
+      ID: 123
+      """
+    And STDOUT should contain:
+      """
+      ID: 456
+      """
+    And STDOUT should contain:
+      """
+      ID: 789
+      """
+
+    # Test on Windows with single ID (should not be split)
+    When I run `WP_CLI_TEST_IS_WINDOWS=1 wp --require=custom-cmd.php test-ids 123`
+    Then STDOUT should contain:
+      """
+      Number of arguments: 1
+      """
+    And STDOUT should contain:
+      """
+      ID: 123
+      """
+
+    # Test on non-Windows (should pass through as-is)
+    When I run `WP_CLI_TEST_IS_WINDOWS=0 wp --require=custom-cmd.php test-ids "123 456"`
+    Then STDOUT should contain:
+      """
+      Number of arguments: 1
+      """
+    And STDOUT should contain:
+      """
+      ID: 123 456
+      """
+
+    # Test on Windows with mixed arguments (non-numeric strings should not be split)
+    When I run `WP_CLI_TEST_IS_WINDOWS=1 wp --require=custom-cmd.php test-ids "hello world"`
+    Then STDOUT should contain:
+      """
+      Number of arguments: 1
+      """
+    And STDOUT should contain:
+      """
+      ID: hello world
+      """
+
   Scenario: Warn when command overrides global argument
     Given an empty directory
     And a custom-cmd.php file:

@@ -979,6 +979,27 @@ public function get_wp_config_code( $wp_config_path = '' ) {
 	 * @return array
 	 */
 	private static function back_compat_conversions( $args, $assoc_args ) {
+		// On Windows (PowerShell), command substitution like $(wp post list --format=ids)
+		// returns space-separated values as a single string argument instead of separate arguments.
+		// Split such arguments to maintain compatibility with Unix-like behavior.
+		if ( Utils\is_windows() ) {
+			$split_args = [];
+			foreach ( $args as $arg ) {
+				// Check if the argument contains space-separated numeric IDs
+				// We only split if the entire argument matches the pattern of space-separated numbers
+				if ( is_string( $arg ) && preg_match( '/^\d+(\s+\d+)+$/', $arg ) ) {
+					// Split on whitespace and add each ID as a separate argument
+					$ids = preg_split( '/\s+/', $arg, -1, PREG_SPLIT_NO_EMPTY );
+					if ( false !== $ids ) {
+						array_push( $split_args, ...$ids );
+					}
+				} else {
+					$split_args[] = $arg;
+				}
+			}
+			$args = $split_args;
+		}
+
 		$top_level_aliases = [
 			'sql'  => 'db',
 			'blog' => 'site',

@@ -0,0 +1,103 @@
+<?php
+
+use PHPUnit\Framework\TestCase;
+use WP_CLI\Runner;
+
+/**
+ * Test Windows PowerShell argument splitting
+ */
+class WindowsArgsTest extends TestCase {
+
+	/**
+	 * Test that space-separated numeric IDs are split on Windows
+	 *
+	 * @dataProvider provideWindowsArguments
+	 */
+	#[PHPUnit\Framework\Attributes\DataProvider( 'provideWindowsArguments' )] // phpcs:ignore PHPCompatibility.Attributes.NewAttributes.PHPUnitAttributeFound
+	public function testWindowsArgumentSplitting( $is_windows, $input_args, $expected_count, $expected_values ) {
+		// Set the Windows environment variable
+		putenv( $is_windows ? 'WP_CLI_TEST_IS_WINDOWS=1' : 'WP_CLI_TEST_IS_WINDOWS=0' );
+
+		$reflection = new ReflectionClass( Runner::class );
+		$method     = $reflection->getMethod( 'back_compat_conversions' );
+		if ( PHP_VERSION_ID < 80100 ) {
+			// @phpstan-ignore method.deprecated
+			$method->setAccessible( true );
+		}
+
+		/**
+		 * @var array{0: array<string>, 1: array<string, string>} $result
+		 */
+		$result              = $method->invoke( null, $input_args, [] );
+		[ $result_args, $_ ] = $result;
+
+		// Verify the results
+		$this->assertCount( $expected_count, $result_args, 'Unexpected number of arguments' );
+
+		foreach ( $expected_values as $index => $expected_value ) {
+			$this->assertEquals( $expected_value, $result_args[ $index ], "Argument at index $index doesn't match" );
+		}
+	}
+
+	public static function provideWindowsArguments() {
+		return [
+			// is_windows, input_args, expected_count, expected_values
+			'Windows: space-separated IDs should be split' => [
+				true,
+				[ 'post', 'delete', '123 456 789' ],
+				5,
+				[ 'post', 'delete', '123', '456', '789' ],
+			],
+			'Windows: single ID should not be split'       => [
+				true,
+				[ 'post', 'delete', '123' ],
+				3,
+				[ 'post', 'delete', '123' ],
+			],
+			'Windows: non-numeric strings should not be split' => [
+				true,
+				[ 'post', 'delete', 'hello world' ],
+				3,
+				[ 'post', 'delete', 'hello world' ],
+			],
+			'Windows: mixed args (numeric at start)'       => [
+				true,
+				[ 'post', 'delete', '123 456', 'some-slug' ],
+				5,
+				[ 'post', 'delete', '123', '456', 'some-slug' ],
+			],
+			'Non-Windows: space-separated IDs should not split' => [
+				false,
+				[ 'post', 'delete', '123 456' ],
+				3,
+				[ 'post', 'delete', '123 456' ],
+			],
+			'Windows: IDs with tabs and spaces'            => [
+				true,
+				[ 'post', 'delete', "123\t456  789" ],
+				5,
+				[ 'post', 'delete', '123', '456', '789' ],
+			],
+			'Windows: normal case without leading/trailing spaces' => [
+				true,
+				[ 'post', 'delete', '123 456' ],
+				4,
+				[ 'post', 'delete', '123', '456' ],
+			],
+			'Windows: leading/trailing spaces prevent splitting' => [
+				true,
+				[ 'post', 'delete', '  123 456  ' ],
+				3,
+				[ 'post', 'delete', '  123 456  ' ],
+			],
+		];
+	}
+
+	/**
+	 * Cleanup after each test
+	 */
+	public function tearDown(): void {
+		putenv( 'WP_CLI_TEST_IS_WINDOWS' );
+		parent::tearDown();
+	}
+}