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Gorav22

TerminusAI

by Gorav22
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TypeScript

execute_command

Execute terminal commands locally or on remote hosts via SSH with session persistence and environment variable support for efficient command workflows.

Instructions

Execute commands on remote hosts or locally (This tool can be used for both remote hosts and the current machine)

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
hostNoHost to connect to (optional, if not provided the command will be executed locally)
usernameNoUsername for SSH connection (required when host is specified)
sessionNoSession name, defaults to 'default'. The same session name will reuse the same terminal environment for 20 minutes, which is useful for operations requiring specific environments like conda.default
commandYesCommand to execute. Before running commands, it's best to determine the system type (Mac, Linux, etc.)
envNoEnvironment variables

Implementation Reference

  • src/executor.ts:128-320 (handler)
    Main handler that executes the command locally or on remote host via SSH, managing persistent sessions, environment variables, and using either interactive shell or exec.
    async executeCommand(
  command: string,
  options: {
    host?: string;
    username?: string;
    session?: string;
    env?: Record<string, string>;
  } = {}
): Promise<{stdout: string; stderr: string}> {
  const { host, username, session = 'default', env = {} } = options;
  const sessionKey = this.getSessionKey(host, session);

  // 如果指定了host，则使用SSH执行命令
  if (host) {
    if (!username) {
      throw new Error('Username is required when using SSH');
    }
    
    let sessionData = this.sessions.get(sessionKey);
    
    let needNewConnection = false;
    if (!sessionData || sessionData.host !== host) {
      needNewConnection = true;
    } else if (sessionData.client) {
      if (sessionData.client.listenerCount('ready') === 0 && sessionData.client.listenerCount('data') === 0) {
        log.info(`Session ${sessionKey} disconnected, reconnecting`);
        needNewConnection = true;
      }
    } else {
      needNewConnection = true;
    }
    
    if (needNewConnection) {
      log.info(`Creating new connection for command execution: ${sessionKey}`);
      await this.connect(host, username, session);
      sessionData = this.sessions.get(sessionKey);
    } else {
      log.info(`Reusing existing session for command execution: ${sessionKey}`);
    }
    
    if (!sessionData || !sessionData.client) {
      throw new Error(`host ${host} err`);
    }
    
    this.resetTimeout(sessionKey);

    if (sessionData.shellReady && sessionData.shell) {
      log.info(`Executing command using interactive shell: ${command}`);
      return new Promise((resolve, reject) => {
        let stdout = "";
        let stderr = "";
        let commandFinished = false;
        const uniqueMarker = `CMD_END_${Date.now()}_${Math.random().toString(36).substring(2, 15)}`;
        
        const envSetup = Object.entries(env)
          .map(([key, value]) => `export ${key}="${String(value).replace(/"/g, '\\"')}"`)
          .join(' && ');
        
        const fullCommand = envSetup ? `${envSetup} && ${command}` : command;
        
        const dataHandler = (data: Buffer) => {
          const str = data.toString();
          log.debug(`Shell数据: ${str}`);
          
          if (str.includes(uniqueMarker)) {
            commandFinished = true;
            
            const lines = stdout.split('\n');
            let commandOutput = '';
            let foundCommand = false;
            
            for (const line of lines) {
              if (foundCommand) {
                if (line.includes(uniqueMarker)) {
                  break;
                }
                commandOutput += line + '\n';
              } else if (line.includes(fullCommand)) {
                foundCommand = true;
              }
            }
            
            resolve({ stdout: commandOutput.trim(), stderr });
            
            sessionData.shell.removeListener('data', dataHandler);
            clearTimeout(timeout);
          } else if (!commandFinished) {
            stdout += str;
          }
        };
        
        const errorHandler = (err: Error) => {
          stderr += err.message;
          reject(err);
          sessionData.shell.removeListener('data', dataHandler);
          sessionData.shell.removeListener('error', errorHandler);
        };
        
        sessionData.shell.on('data', dataHandler);
        sessionData.shell.on('error', errorHandler);
        
        sessionData.shell.write(`echo "Starting command execution: ${fullCommand}"\n`);
        sessionData.shell.write(`${fullCommand}\n`);
        sessionData.shell.write(`echo "${uniqueMarker}"\n`);
        
        const timeout = setTimeout(() => {
          if (!commandFinished) {
            stderr += "Command execution timed out";
            resolve({ stdout, stderr });
            sessionData.shell.removeListener('data', dataHandler);
            sessionData.shell.removeListener('error', errorHandler);
          }
        }, 30000); // 30 seconds
      });
    } else {
      log.info(`Executing command using exec: ${command}`);
      return new Promise((resolve, reject) => {
        const envSetup = Object.entries(env)
          .map(([key, value]) => `export ${key}="${String(value).replace(/"/g, '\\"')}"`)
          .join(' && ');
        
        const fullCommand = envSetup ? `${envSetup} && ${command}` : command;
        
        sessionData?.client?.exec(`/bin/bash --login -c "${fullCommand.replace(/"/g, '\\"')}"`, (err, stream) => {
          if (err) {
            reject(err);
            return;
          }

          let stdout = "";
          let stderr = '';

          stream
            .on("data", (data: Buffer) => {
              this.resetTimeout(sessionKey);
              stdout += data.toString();
            })
            .stderr.on('data', (data: Buffer) => {
              stderr += data.toString();
            })
            .on('close', () => {
              resolve({ stdout, stderr });
            })
            .on('error', (err) => {
              reject(err);
            });
        });
      });
    }
  } 
  else {
    log.info(`Executing command using local session: ${sessionKey}`);
    
    let sessionData = this.sessions.get(sessionKey);
    let sessionEnv = {};
    
    if (!sessionData) {
      sessionData = {
        client: null,
        connection: null,
        timeout: null,
        host: undefined,
        env: { ...env } 
      };
      this.sessions.set(sessionKey, sessionData);
      log.info(`Creating new local session: ${sessionKey}`);
      sessionEnv = env;
    } else {
      log.info(`Reusing existing local session: ${sessionKey}`);
      if (!sessionData.env) {
        sessionData.env = {};
      }
      sessionData.env = { ...sessionData.env, ...env };
      sessionEnv = sessionData.env;
      this.sessions.set(sessionKey, sessionData);
    }
    
    this.resetTimeout(sessionKey);
    
    return new Promise((resolve, reject) => {
      const envVars = { ...process.env, ...sessionEnv };
      
      log.info(`Executing local command: ${command}`);
      exec(command, { env: envVars }, (error, stdout, stderr) => {
        if (error && error.code !== 0) {
          resolve({ stdout, stderr: stderr || error.message });
        } else {
          resolve({ stdout, stderr });
        }
      });
    });
  }
}
  • src/index.ts:49-75 (schema)
    Input schema definition for the execute_command tool, specifying parameters like host, username, session, command, and env.
    inputSchema: {
  type: "object",
  properties: {
    host: {
      type: "string",
      description: "Host to connect to (optional, if not provided the command will be executed locally)"
    },
    username: {
      type: "string",
      description: "Username for SSH connection (required when host is specified)"
    },
    session: {
      type: "string",
      description: "Session name, defaults to 'default'. The same session name will reuse the same terminal environment for 20 minutes, which is useful for operations requiring specific environments like conda.",
      default: "default"
    },
    command: {
      type: "string",
      description: "Command to execute. Before running commands, it's best to determine the system type (Mac, Linux, etc.)"
    },
    env: {
      type: "object",
      description: "Environment variables",
      default: {}
    }
  },
  required: ["command"]
  • src/index.ts:43-80 (registration)
    Registers the execute_command tool in the MCP server's ListToolsRequest handler by providing its name, description, and schema.
    server.setRequestHandler(ListToolsRequestSchema, async () => {
  return {
    tools: [
      {
        name: "execute_command",
        description: "Execute commands on remote hosts or locally (This tool can be used for both remote hosts and the current machine)",
        inputSchema: {
          type: "object",
          properties: {
            host: {
              type: "string",
              description: "Host to connect to (optional, if not provided the command will be executed locally)"
            },
            username: {
              type: "string",
              description: "Username for SSH connection (required when host is specified)"
            },
            session: {
              type: "string",
              description: "Session name, defaults to 'default'. The same session name will reuse the same terminal environment for 20 minutes, which is useful for operations requiring specific environments like conda.",
              default: "default"
            },
            command: {
              type: "string",
              description: "Command to execute. Before running commands, it's best to determine the system type (Mac, Linux, etc.)"
            },
            env: {
              type: "object",
              description: "Environment variables",
              default: {}
            }
          },
          required: ["command"]
        }
      }
    ]
  };
});
  • src/index.ts:82-133 (handler)
    MCP CallTool request handler specific to execute_command, validates params, invokes CommandExecutor, and formats response.
    server.setRequestHandler(CallToolRequestSchema, async (request) => {
  try {
    if (request.params.name !== "execute_command") {
      throw new McpError(ErrorCode.MethodNotFound, "Unknown tool");
    }
    
    const host = request.params.arguments?.host ? String(request.params.arguments.host) : undefined;
    const username = request.params.arguments?.username ? String(request.params.arguments.username) : undefined;
    const session = String(request.params.arguments?.session || "default");
    const command = String(request.params.arguments?.command);
    if (!command) {
      throw new McpError(ErrorCode.InvalidParams, "Command is required");
    }
    const env = request.params.arguments?.env || {};

    if (host && !username) {
      throw new McpError(ErrorCode.InvalidParams, "Username is required when host is specified");
    }

    try {
      const result = await commandExecutor.executeCommand(command, {
        host,
        username,
        session,
        env: env as Record<string, string>
      });
      
      return {
        content: [{
          type: "text",
          text: `Command Output:\nstdout: ${result.stdout}\nstderr: ${result.stderr}`
        }]
      };
    } catch (error) {
      if (error instanceof Error && error.message.includes('SSH')) {
        throw new McpError(
          ErrorCode.InternalError,
          `SSH connection error: ${error.message}. Please ensure SSH key-based authentication is set up.`
        );
      }
      throw error;
    }
  } catch (error) {
    if (error instanceof McpError) {
      throw error;
    }
    throw new McpError(
      ErrorCode.InternalError,
      error instanceof Error ? error.message : String(error)
    );
  }
});

Tool Definition Quality

C2.9/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries full burden but lacks critical behavioral details. It mentions remote/local execution but doesn't disclose permissions needed, security implications, rate limits, error handling, or output format. For a command execution tool, this is a significant gap in transparency.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is concise and front-loaded with the core purpose in the first phrase. The parenthetical adds useful context without redundancy. However, it could be slightly more structured by separating key points into distinct sentences for clarity.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's complexity (command execution with security implications), no annotations, and no output schema, the description is incomplete. It lacks details on behavioral traits, error handling, output format, and safety considerations, making it inadequate for informed use.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema fully documents all 5 parameters. The description adds no parameter-specific semantics beyond what's in the schema, such as examples or usage nuances. Baseline 3 is appropriate when schema does the heavy lifting.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's purpose: 'Execute commands on remote hosts or locally' with the parenthetical adding specificity about both remote and local execution. It uses a specific verb ('Execute') and resource ('commands'), but without sibling tools, differentiation isn't applicable.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides no guidance on when to use this tool versus alternatives, prerequisites, or typical use cases. It only restates the scope (remote/local) without addressing scenarios, constraints, or best practices for command execution.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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