Shell-MCP

Instructions

Implementation Reference

• src/index.ts:27-43 (registration)

  Registers the 'shell_echo' tool (from 'shell.echo' config) with input schema for arguments array. Transforms config key 'shell.echo' to tool name 'shell_echo'.
  server.setRequestHandler(ListToolsRequestSchema, async () => { const tools = Object.entries(allowedCommands).map(([name, config]) => ({ name: name.replace('shell.', 'shell_'), // Replace shell. with shell_ description: config.description, inputSchema: { type: "object", properties: { args: { type: "array", items: { type: "string" }, description: "Command arguments" } } } })); return { tools }; });
• src/index.ts:45-85 (handler)

  Executes the 'shell_echo' tool by mapping 'shell_echo' to 'shell.echo' config, extracting 'echo' command, validating args, executing via spawn, and returning stdout as text content.
  server.setRequestHandler(CallToolRequestSchema, async (request) => { try { const command = String(request.params?.name || ''); const fullCommand = `shell.${command.replace('shell_', '')}`; // Replace shell_ back to shell. if (!(fullCommand in allowedCommands)) { return { content: [{ type: "text", text: `Unknown command: ${command}` }], isError: true }; } const actualCommand = allowedCommands[fullCommand].command; const args = Array.isArray(request.params?.arguments?.args) ? request.params.arguments.args.map(String) : []; validator.validateCommand(actualCommand, args); const stream = await executor.execute(actualCommand, args); return { content: [{ type: "text", text: await new Promise((resolve, reject) => { const chunks: Buffer[] = []; stream.stdout.on('data', (chunk: Buffer) => chunks.push(chunk)); stream.stdout.on('end', () => resolve(Buffer.concat(chunks).toString())); stream.stdout.on('error', reject); }) }] }; } catch (error) { return { content: [{ type: "text", text: `Command execution failed: ${error instanceof Error ? error.message : String(error)}` }], isError: true }; } });
• src/config/allowlist.ts:38-42 (registration)

  Allowlist configuration enabling the 'shell.echo' command (maps to tool 'shell_echo'), specifying the underlying 'echo' binary, description, and timeout.
  'shell.echo': { command: 'echo', description: 'Display text', timeout: 1000 },
• src/core/executor.ts:31-139 (handler)

  Core execution logic that spawns the 'echo' process with arguments as child_process, providing stdout stream. Used by the MCP handler for 'shell_echo'.
  async execute( command: string, args: string[] = [], options: ExecuteOptions = {} ): Promise<{ stdout: Readable }> { const commandKey = `${command} ${args.join(' ')}`; try { // Check security await this.securityChecker.validateCommand(command, args, options); // Check cache const cached = this.cache.get(commandKey); if (cached) { this.logger.debug('Using cached command result', { command, args }); return this.createStreamFromCache(cached); } // Remove 'shell.' prefix for execution const baseCommand = command.replace('shell.', ''); // Execute command this.logger.debug('Starting command execution', { command, args, options }); const childProcess = spawn(baseCommand, args, { stdio: ['ignore', 'pipe', 'pipe'], timeout: options.timeout, cwd: options.cwd, env: { ...process.env, ...options.env }, signal: options.signal }); this.currentProcess = childProcess; // Error handling childProcess.on('error', (error: Error) => { this.logger.error('Command execution error', { command, args, error: error.message }); throw new ToolError( 'PROCESS_ERROR', 'Command execution error', { command, args, error: error.message } ); }); // Timeout handling if (options.timeout) { setTimeout(() => { if (childProcess.exitCode === null) { this.logger.warn('Command execution timeout', { command, args, timeout: options.timeout }); childProcess.kill(); throw new ToolError( 'TIMEOUT', 'Command execution timeout', { command, args, timeout: options.timeout } ); } }, options.timeout); } if (!childProcess.stdout) { throw new ToolError( 'STREAM_ERROR', 'Unable to get command output stream', { command, args } ); } // Monitor process status childProcess.on('exit', (code, signal) => { this.logger.debug('Command execution completed', { command, args, exitCode: code, signal }); }); return { stdout: childProcess.stdout }; } catch (error) { this.logger.error('Command execution failed', { command, args, error: error instanceof Error ? error.message : String(error) }); throw new ToolError( 'EXECUTION_ERROR', 'Command execution failed', { command, args, error: error instanceof Error ? error.message : String(error) } ); } }