Executing Local Shell Scripts Remotely via SSH

Introduction

Secure Shell (SSH) is a powerful tool for securely connecting to remote systems and executing commands. One practical application of SSH is running local shell scripts on a remote machine without having to transfer the script itself. This tutorial will guide you through different methods of achieving this, focusing on both Windows and Unix-based systems.

Prerequisites

• SSH Configuration: Ensure that SSH is configured on both your local machine (Machine A) and the target remote machine (Machine B).
• Access Credentials: You need appropriate access credentials for Machine B.
• Script Readiness: Have a shell script ready on Machine A you wish to execute remotely.

Method 1: Using Plink on Windows

If your local machine is running Windows, PuTTY provides plink, a command-line interface to SSH. Here’s how to run a local script on a remote Unix-based system:

plink root@MachineB -m local_script.sh

• Parameters:
  • -m: Specifies the local script file to execute.
  • Replace root@MachineB with your actual username and hostname/IP of Machine B.

Method 2: Using SSH on Unix-based Systems

For Unix or Linux systems, you can leverage the SSH command-line client:

ssh user@MachineB 'bash -s' < local_script.sh

• Parameters:
  • user@MachineB: Your username and Machine B’s address.
  • 'bash -s': Invokes a new bash shell on Machine B to read from standard input.

Method 3: Using SSH with Here Documents

Here documents allow you to embed multiple commands within an SSH session. This is particularly useful for running complex scripts:

ssh user@host << 'ENDSSH'
# Commands to run on the remote host
echo "Hello, World!"
ENDSSH

• Features:
  • Supports nesting of commands.
  • Useful for multi-step operations or when requiring user input.

Method 4: Passing Environment Variables

To make your script more dynamic, you can pass environment variables from your local machine to the remote system:

ssh user@host ARG1=value1 ARG2=value2 'bash -s' << 'ENDSSH'
  echo $ARG1 $ARG2
ENDSSH

• Benefits:
  • Facilitates parameterization of scripts.
  • Enhances script reusability and maintainability.

Best Practices

• Secure Access: Use SSH keys for passwordless authentication. Ensure your public key is added to the authorized_keys file on Machine B.

• Quoting Variables: When dealing with variables in a remote shell, use proper quoting to avoid unexpected substitutions:

  ssh user@host "echo \$HOME"
  

  This ensures that $HOME from the local context does not get substituted prematurely.

Conclusion

Running local scripts on a remote machine via SSH is efficient and secure. Whether you’re working in Windows or Unix environments, these methods offer flexibility and convenience. Understanding how to pass variables and use here documents can significantly enhance your scripting capabilities over SSH.