feat: Add Shell Command Execution to Custom Commands (#4917)

packages/cli/src/services/prompt-processors/shellProcessor.ts

@@ -0,0 +1,106 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import {
+  checkCommandPermissions,
+  ShellExecutionService,
+} from '@google/gemini-cli-core';
+
+import { CommandContext } from '../../ui/commands/types.js';
+import { IPromptProcessor } from './types.js';
+
+export class ConfirmationRequiredError extends Error {
+  constructor(
+    message: string,
+    public commandsToConfirm: string[],
+  ) {
+    super(message);
+    this.name = 'ConfirmationRequiredError';
+  }
+}
+
+/**
+ * Finds all instances of shell command injections (`!{...}`) in a prompt,
+ * executes them, and replaces the injection site with the command's output.
+ *
+ * This processor ensures that only allowlisted commands are executed. If a
+ * disallowed command is found, it halts execution and reports an error.
+ */
+export class ShellProcessor implements IPromptProcessor {
+  /**
+   * A regular expression to find all instances of `!{...}`. The inner
+   * capture group extracts the command itself.
+   */
+  private static readonly SHELL_INJECTION_REGEX = /!\{([^}]*)\}/g;
+
+  /**
+   * @param commandName The name of the custom command being executed, used
+   *   for logging and error messages.
+   */
+  constructor(private readonly commandName: string) {}
+
+  async process(prompt: string, context: CommandContext): Promise<string> {
+    const { config, sessionShellAllowlist } = {
+      ...context.services,
+      ...context.session,
+    };
+    const commandsToExecute: Array<{ fullMatch: string; command: string }> = [];
+    const commandsToConfirm = new Set<string>();
+
+    const matches = [...prompt.matchAll(ShellProcessor.SHELL_INJECTION_REGEX)];
+    if (matches.length === 0) {
+      return prompt; // No shell commands, nothing to do.
+    }
+
+    // Discover all commands and check permissions.
+    for (const match of matches) {
+      const command = match[1].trim();
+      const { allAllowed, disallowedCommands, blockReason, isHardDenial } =
+        checkCommandPermissions(command, config!, sessionShellAllowlist);
+
+      if (!allAllowed) {
+        // If it's a hard denial, this is a non-recoverable security error.
+        if (isHardDenial) {
+          throw new Error(
+            `${this.commandName} cannot be run. ${blockReason || 'A shell command in this custom command is explicitly blocked in your config settings.'}`,
+          );
+        }
+
+        // Add each soft denial disallowed command to the set for confirmation.
+        disallowedCommands.forEach((uc) => commandsToConfirm.add(uc));
+      }
+      commandsToExecute.push({ fullMatch: match[0], command });
+    }
+
+    // If any commands require confirmation, throw a special error to halt the
+    // pipeline and trigger the UI flow.
+    if (commandsToConfirm.size > 0) {
+      throw new ConfirmationRequiredError(
+        'Shell command confirmation required',
+        Array.from(commandsToConfirm),
+      );
+    }
+
+    // Execute all commands (only runs if no confirmation was needed).
+    let processedPrompt = prompt;
+    for (const { fullMatch, command } of commandsToExecute) {
+      const { result } = ShellExecutionService.execute(
+        command,
+        config!.getTargetDir(),
+        () => {}, // No streaming needed.
+        new AbortController().signal, // For now, we don't support cancellation from here.
+      );
+
+      const executionResult = await result;
+      processedPrompt = processedPrompt.replace(
+        fullMatch,
+        executionResult.output,
+      );
+    }
+
+    return processedPrompt;
+  }
+}