Scripting is a very useful skill which will save any Sysadmin a lot of time. Who wants to go to every device in their environment and perform the same task over and over again? In this posting I will cover a few basics for those getting started in scripting.

When writing a script you want to be sure it is:

1. Readable
2. Reusable
3. Full of Comments
4. Properly handle errors

When you think about it; writing scripts is not all that different from developing software. You are writing a bit of code for the computer to interpret in order to complete a task. You script may or may not have anything visible on the screen, but same goes for software you may write.

The main difference between a script and a program is a script is interpreted and a program is compiled then executed. A script you can modify with a text editor, then run immediately. A program you must modify, re-compile, then re-run. You might even use the same languages when scripting vs programming. Other than this minor difference, they are really the same thing; so the same principles should apply when developing your scripts.

Throughout this article, I will use some Python code to give examples when applicable

Lets go through our bullet points:

Writing Readable Scripts

Ensuring your script is readable is essential for both you and others who may need to understand or modify it later. Readable scripts facilitate easier troubleshooting and updates, especially as changes occur in your operational environment.

While an entire article could be dedicated to the nuances of creating readable scripts, a key starting point is to observe and learn from existing scripts. Take note of how experienced scripters format their code and organize their logic. This observation can provide valuable insights into what makes a script easy to understand and what complicates comprehension.

Tips for Enhancing Script Readability:

• Consistent Formatting: Use a consistent style for indentations, line breaks, and other formatting elements. Tools like linters can automate and standardize formatting to reduce the cognitive load on the reader.
• Descriptive Naming: Choose variable and function names that clearly indicate their purpose. Avoid cryptic abbreviations; names should be self-explanatory to someone reading your code.
• Logical Structuring: Organize your script logically. Group related operations together and separate distinct sections clearly, which helps in tracing through the script’s flow more intuitively.
• Minimal Complexity: Keep the script as simple as possible. Break complex operations into smaller functions if they perform multiple steps or calculations.

By applying these practices, you make your scripts more accessible not only to others but also to your future self, ensuring that maintenance and troubleshooting can be conducted more smoothly and efficiently.

Making your scripts reusable

Investing time in scripting can yield significant time savings, turning a task that might take days into one that takes just seconds. To maximize the return on this investment, it’s beneficial to write scripts with reusability in mind. This means crafting your script so it can be easily adapted for future tasks, which may be similar yet distinct.

Here are some strategies to enhance the reusability of your scripts:

Modularize with Functions

Functions or subroutines are your best friends when it comes to building reusable scripts. By encapsulating specific functionalities into functions, you create modular blocks of code that can be easily lifted and shifted into new scripts as needed.

For example, imagine you have a script designed to delete files older than 5 days. Within this script, you might include a function to determine the age of the files. When you later decide to create a script to report on files of similar age without deleting them, you can reuse the same age-calculation function. This not only saves time but also maintains consistency across your scripts, reducing the likelihood of errors when rewriting similar logic.

Employ Variables Effectively

Avoid hard-coding values directly into your scripts. Instead, use variables to represent these values. This approach offers flexibility and makes your scripts more adaptable to changes without extensive rewrites.

Continuing with the previous example, if you initially set your script to delete files older than 5 days using a hard-coded value, modifying this to accommodate a new requirement of 7 days would be cumbersome and error-prone. By using a variable to store the age threshold, you only need to update the variable’s value to change the script’s behavior. This change propagates through all parts of your script where the variable is used, streamlining updates and maintenance.

Benefits of Reusable Scripts

• Efficiency: Save time and effort on future tasks by reusing code.
• Consistency: Maintain consistent logic across multiple scripts, reducing the risk of errors.
• Maintainability: Simplify updates and modifications to scripts as requirements evolve.

By focusing on these aspects of scripting, you not only make your life easier but also enhance the quality and longevity of your scripts. Whether you’re automating routine tasks or building complex systems, reusability should be a cornerstone of your scripting strategy.

Importance of comments in scripting

Comments are a vital part of writing clear, maintainable scripts. They help you and others understand the purpose, logic, and flow of the code even months after it was originally written. Well-commented code is especially crucial in a collaborative environment or when you’re likely to revisit your own code after a long period. Here’s how to effectively integrate comments into your scripting.

Why Comment Your Scripts?

• Clarity: Comments clarify what the code does, making it easier for others (or yourself) to follow along and understand the intended logic without having to decipher every line of code.
• Maintenance: Well-commented code is easier to debug and update. Clear comments can guide developers through necessary changes or troubleshooting without introducing new errors.
• Documentation: In many cases, comments in the script can serve as documentation for the code itself, explaining why certain decisions were made or detailing the usage of specific functions or parameters.

How to Write Effective Comments

Descriptive Comments: Before blocks of code, write comments that describe what the code does and why it’s necessary. This is helpful for blocks of code that perform specific functions.

# Check if the file exists before attempting to delete
if os.path.exists(file_path):
    os.remove(file_path)
else:
    print(f"No file found at {file_path}")

Inline Comments: Use inline comments sparingly to clarify complex lines of code or unusual solutions that are not immediately obvious.

x = y + z  # Increment x by the sum of y and z for the next loop iteration

Function and Module Comments: At the beginning of every function or module, use comments to explain the purpose, inputs, outputs, and any side effects.

def delete_old_files(path, days=5):
    """
    Delete files older than a specified number of days.
    Parameters:
    path (str): Directory path to search for files.
    days (int): Number of days old a file must be to be deleted.
    """

TODO Comments: If you’re in the middle of working on a script and need to leave notes for future tasks, use TODO comments to highlight areas that need further development or attention.

TODO: Implement error handling for file access permissions

Avoid Obvious Comments: Don’t over-comment by stating the obvious. Comments should add value and provide insight, not just reiterate what the code clearly says.

# BAD: Set x to 1
x = 1

# GOOD: Initialize x with the starting value for the counter
x = 1

Commenting Best Practices

• Consistency: Be consistent with your commenting style throughout your script. This includes the placement of comments, the language used, and the level of detail provided.
• Maintenance: Regularly review and update comments when you modify the code. Outdated comments can be more misleading than no comments at all.
• Educational Use: Use comments to explain complex algorithms or logic to help anyone who’s learning the code or the programming concepts involved.

By adhering to these practices, you ensure that your scripts are not only functional but also understandable and maintainable. Remember, writing comments is not just about documenting what the code does; it’s about making the code accessible and easier to manage for anyone who might work on it after you.

Properly handle errors

When developing scripts, it’s crucial to implement error handling to ensure that your scripts can gracefully handle unexpected situations without crashing. Effective error handling can provide stability and reliability in automated tasks, especially in a production environment. Here’s how to approach error handling in your scripts:

Understanding Error Handling

Error handling refers to the process of anticipating, detecting, and responding to exceptions or errors in a script. Without proper error handling, scripts might fail in unpredictable ways, possibly causing more damage or downtime. By managing errors appropriately, you can ensure that your script either recovers from the error or fails safely.

Basic Error Handling Techniques

Try-Catch Blocks: Most scripting languages support try-catch blocks, which allow you to “try” a block of code and “catch” any errors that occur within it. Here’s a simple example in Python:

try:
    # Attempt to open a file
    with open('config.txt', 'r') as file:
        data = file.read()
except FileNotFoundError:
    print("Error: File not found.")
except Exception as e:
    print(f"An error occurred: {str(e)}")

In this example, if the file config.txt does not exist, the script catches the FileNotFoundError and handles it by printing a specific message. Any other exceptions are caught by the general Exception class.

Checking Return Values: Some functions return specific values or codes when they fail. You can check these values to determine if an error occurred:

cp /source/file.txt /dest/
if [ $? -ne 0 ]; then
    echo "Failed to copy file."
fi

In this Bash script example, $? captures the exit status of the last command executed (cp). If the copy operation fails, it returns a non-zero status, triggering the error message.

Validating Preconditions: Before performing actions, validate that all necessary conditions are met. This could involve checking for the existence of files, the validity of inputs, or network connectivity:

import os

if not os.path.isfile('config.txt'):
    print("Error: config.txt is missing.")
    exit(1)  # Exit the script with an error code

Advanced Error Handling Strategies

• Logging: Instead of simply printing errors, log them to a file. This helps in troubleshooting and maintaining records of what went wrong. Python’s logging library can be used for this purpose.
• Retry Mechanisms: For errors that might resolve on their own (like network issues), implement a retry mechanism. This could involve retrying a failed operation multiple times with a delay between attempts.
• Custom Error Classes: For more complex scripts, define custom error classes. This allows you to handle specific types of errors more granularly.

Best Practices for Error Handling

• Be Specific: Catch specific exceptions rather than general exceptions wherever possible. This helps in accurately identifying the problem.
• Fail Safely: If recovery from an error is not possible, ensure the script fails in a way that does not cause additional problems. Clean up resources, close connections, and inform the user or a logging system about the issue.
• Document Error Handling: Document how your script handles errors, including any assumptions or dependencies that affect error management.

By integrating robust error handling into your scripts, you can build more resilient and reliable systems that minimize downtime and maintain productivity even when unexpected events occur.

Summary

Hopefully this article has been helpful to you. I have gone over a few basics to consider when you start scripting. In the future I will go more in-depth about the concepts. Be sure to check back to the site as I will be posting scripts for performing various tasks.