Best Practices for Writing Effective Bash Scripts Usable by Other Users

Shell scripts are powerful tools for automating tasks and managing systems. However, to ensure your scripts are robust, reusable, and user-friendly, it's crucial to follow best practices in shell programming. This article delves into these practices, offering guidance on how to create Bash scripts that can be effectively utilized by other users.

External Validation: Ensuring Safety and Reliability

When it comes to external validation, your Bash script must be robust to handle various inputs and situations:

Validate the Invocation

Ensure that the script:

Checks for disallowed combinations of options, especially those that require other options. Validates options that require other options to be provided. Verifies the existence and readability of input files provided via command-line parameters. Avoids exiting at the first sign of an error, but logs all errors to ensure a comprehensive issue report.

Input Validation

Thoroughly validate all inputs, including:

Command-line parameters Environment variables Interactive input Information read from files other than those bundled with the script

Quote variable dereferences that could encompass user input or contain white spaces, shell meta-characters, etc., except for variables computed from validated inputs known to be alphanumeric or integers.

Using Shell Best Practices

Adopting good practices in shell scripting can significantly enhance the usability and reliability of your scripts:

Managing Temporary Files

Use mktemp to create temporary files and ensure they are deleted properly using the built-in trap command.

Handling Signals and Termination

Implement signal and termination handling appropriately. For example, SIGINT (^C) might require special treatment either by catching it or ignoring it.

Support Customization Options

Consider providing options for:

An environment variable that supplies extra parameters interpreted before the command-line arguments. A .rc file that interprets parameters before both the environment variable and command-line arguments.

Portability Considerations

Adapt to different environments if portability is a requirement:

Check and test the execution environment. Use procedural encapsulation to manage differences between supported environments.

Always return an appropriate exit code to signal the success or failure of the script execution.

Internal Practices for Code Quality

Ensure code quality through explicit variable declarations and procedural encapsulation:

Variable Declarations

Explicitly declare all variables, especially:

Arrays Integers

Use local for procedure-local variables rather than declare.

Consider enabling set -u / set -o nounset to enforce the presence of all variables before they are used.

Validate select internal values where necessary, and keep all constants in variables, not hard-coded in the script.

Avoid Code Duplication

Use procedural encapsulation to avoid code duplication, ensuring a clean and maintainable script.

Do not place commands directly in trap invocations. Instead, define a procedure and pass it to trap.

Conclusion

Shell scripts are just as important as any other program, and they deserve the same level of care in design and coding. By following these best practices, you can create robust, reusable, and user-friendly Bash scripts that will serve your needs and those of other users effectively.