Cheatsheet - Shell Scripting

Shell Scripting Guide Cheatsheet

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Overview

Bash scripting offers a wide range of commands that can be used to perform various tasks.

Here are some of the most commonly used ones:

1. echo: Used to print text or data to the terminal. It’s often used for printing variable values or messages. ()
2. read: Used to read input from the user. This is often used to get user input during script execution.
3. cd: Changes the current directory. This is used to navigate through the file system.
4. ls: Lists all files and directories in the current directory.
5. pwd: Prints the path of the current directory.
6. touch: Creates a new empty file.
7. cp: Copies files or directories.
8. mv: Moves or renames files or directories.
9. rm: Removes files or directories.
10. cat: Concatenates and displays the content of files.
11. grep: Searches for a specific pattern in files. (See grep)
12. find: Searches for files and directories based on a given expression.
13. chmod: Changes the permissions of a file or directory.
14. chown: Changes the owner and group of a file or directory.
15. export: Sets an environment variable.
16. if, else, elif, fi: Used for conditional statements.
17. for, while, do, done: Used for looping constructs.
18. case, esac: Used for pattern matching and selection constructs.
19. function: Defines a bash function.
20. exit: Exits the shell or your script, can include a status message.

INFO

Remember, each of these commands has its own set of options and arguments that can be used to modify its behavior. You can use the man command followed by the command name to get more information about each command. For example, man ls will give you the manual page for the ls command.

Best Practices

Writing efficient and reliable Bash scripts involves following a set of best practices. Here are some of them:

1. Use Shebang: Always start your script with a shebang (#!/bin/bash) at the top. This tells the system that the script should be executed with Bash.

2. Set ‘Strict’ Mode: Include set -euo pipefail at the beginning of your scripts. This causes the script to exit if any variables are uninitialized (set -u), if any command exits with a non-zero status (set -e), or if a command in a pipeline fails (set -o pipefail).

3. Quote Your Variables: Always quote your variables ("$var" not $var). This prevents word splitting and globbing, and it’s especially important for handling arguments and filenames with spaces.

4. Use Functions: Functions can make your scripts more organized and reusable. They also reduce code duplication.

5. Handle Errors: Always check the exit status of commands and handle errors appropriately. You can use if, else, elif, and case statements to handle different exit statuses.

6. Use Local Variables in Functions: Use the local keyword in functions to avoid variable scope issues.

7. Avoid Using eval: The eval command can be dangerous because it executes arbitrary code. Avoid using it unless absolutely necessary.

8. Use Arrays: If you need to store multiple values, use arrays. They are more efficient and easier to manage than using multiple variables.

9. Use printf Instead of echo: printf is more reliable and flexible than echo for printing formatted output.

10. Comment Your Code: Always comment your code to explain what it does. This makes it easier for others (and future you) to understand.

11. Check for Command Existence: If your script depends on certain commands being available, check for their existence at the start of the script.

12. Use Long Options in Scripts: Long options (--option instead of -o) improve readability of your script.

Remember, the goal is to write scripts that are easy to read, understand, and maintain. Following these best practices can help you achieve that.

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Appendix

Note created on 2024-04-15 and last modified on 2024-04-15.

See Also

Backlinks

LIST FROM [[Cheatsheet - Shell Scripting]] AND -"CHANGELOG" AND -"04-RESOURCES/Cheatsheets/Cheatsheet - Shell Scripting"

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