How can I replace one substring with another string in a shell script?

To replace one substring with another in a shell script:

1. Shell Built-in (Parameter Expansion): Modern shells like bash and zsh allow substring replacement directly using parameter expansion. This is a simple, efficient method for straightforward replacements.
2. Using sed: The sed command is great for replacing text in strings, files, or streams. You can replace the first occurrence of a substring or all occurrences by specifying a flag.
3. Using awk: The awk command is a versatile text-processing tool that can substitute text in strings or files. It is particularly useful for more complex replacements.
4. Using tr: If you’re only replacing individual characters, tr provides a quick way to handle such substitutions.
5. Using perl: For advanced text manipulations or when working with regular expressions, perl is highly powerful and flexible.

Each method has its strengths, so choose the one that best fits your complexity, readability, and efficiency needs.