diff --git a/core/src/code_executors/unsafe_local_code_executor.ts b/core/src/code_executors/unsafe_local_code_executor.ts
index 97061719a..56da44a93 100644
--- a/core/src/code_executors/unsafe_local_code_executor.ts
+++ b/core/src/code_executors/unsafe_local_code_executor.ts
@@ -38,6 +38,14 @@ const POWERSHELL_BASE_ARGS = [
  */
 const CMD_BASE_ARGS = ['/D', '/c'] as const;
 
+/**
+ * Whether `commandPath` names Windows PowerShell (`powershell`) or PowerShell
+ * 7+ (`pwsh`). `path.win32` splits on both separators on every platform.
+ */
+function isPowerShellCommand(commandPath: string): boolean {
+  return /^(powershell|pwsh)(\.exe)?$/i.test(path.win32.basename(commandPath));
+}
+
 /**
  * Options for UnsafeLocalCodeExecutor.
  */
@@ -56,6 +64,10 @@ export interface UnsafeLocalCodeExecutorOptions {
   pythonCommandPath?: string;
   /**
    * The command to run Shell code. Default is `bash`.
+   *
+   * When it names `powershell` or `pwsh` (with or without `.exe`) the script
+   * is written as `.ps1` and run through PowerShell rather than as a bare
+   * shell script.
    */
   shellCommandPath?: string;
 }
@@ -100,6 +112,9 @@ function getExtensionForLanguage(
   }
 
   if (language === CodeExecutionLanguage.SHELL) {
+    if (shellCommandPath && isPowerShellCommand(shellCommandPath)) {
+      return '.ps1';
+    }
     if (IS_WINDOWS) {
       if (shellCommandPath && shellCommandPath.toLowerCase().includes('cmd')) {
         return '.bat';
@@ -189,7 +204,7 @@ export class UnsafeLocalCodeExecutor extends BaseCodeExecutor {
         command = this.pythonCommandPath;
       } else if (language === CodeExecutionLanguage.SHELL) {
         command = this.shellCommandPath;
-        if (this.shellCommandPath.toLowerCase().includes('powershell')) {
+        if (isPowerShellCommand(this.shellCommandPath)) {
           args = [...POWERSHELL_BASE_ARGS, filePath];
         } else if (this.shellCommandPath.toLowerCase().includes('cmd')) {
           args = [...CMD_BASE_ARGS, filePath];
diff --git a/core/test/code_executors/unsafe_local_code_executor_test.ts b/core/test/code_executors/unsafe_local_code_executor_test.ts
index 82a0d2d01..341913ece 100644
--- a/core/test/code_executors/unsafe_local_code_executor_test.ts
+++ b/core/test/code_executors/unsafe_local_code_executor_test.ts
@@ -445,5 +445,49 @@ describe('UnsafeLocalCodeExecutor', () => {
         expect.anything(),
       );
     });
+
+    describe('shell command detection', () => {
+      async function runShellCode(shellCommandPath: string) {
+        await new UnsafeLocalCodeExecutor({shellCommandPath}).executeCode({
+          invocationContext,
+          codeExecutionInput: {
+            code: 'echo "test"',
+            language: CodeExecutionLanguage.SHELL,
+            inputFiles: [],
+          },
+        });
+      }
+
+      it.each([
+        'pwsh',
+        'pwsh.exe',
+        '/usr/bin/pwsh',
+        'C:\\Program Files\\PowerShell\\7\\pwsh.exe',
+        'PWSH',
+        'powershell',
+        'powershell.exe',
+      ])('runs a .ps1 script through PowerShell for %s', async (shell) => {
+        await runShellCode(shell);
+
+        expect(spawnMock).toHaveBeenCalledWith(
+          shell,
+          EXPECTED_POWERSHELL_ARGS,
+          expect.anything(),
+        );
+      });
+
+      it.each([
+        '/opt/pwsh-tools/bin/bash',
+        '/usr/local/powershell-helpers/run.sh',
+      ])('does not treat %s as PowerShell', async (shell) => {
+        await runShellCode(shell);
+
+        expect(spawnMock).toHaveBeenCalledWith(
+          shell,
+          [expect.stringMatching(/script\.(sh|ps1)$/)],
+          expect.anything(),
+        );
+      });
+    });
   });
 });