a - Case conversion with parameter expansion case conversion is converting strings to uppercase or lowercase It can be performed using several methods, depending on the shell and the context of the script 1. with Parameter Expansion ^^ and ,, Pros: Clean and readable. Fast and efficient. No external commands needed. Cons: Not portable to non-Bash shells (like dash, ksh, or zsh without set -o extglob). Not POSIX-compliant. 2. Using tr Pros: Works in any shell that supports tr. Portable and widely available on UNIX systems. Cons: Requires invoking an external command. Less efficient for large-scale operations.
b - Case conversion with awk and sed 3. using awk Pros: Can handle more complex string manipulation. Portable across shells. Cons: Slightly slower than tr or parameter expansion. Requires external command awk. 4. Using sed Pros: Highly flexible for advanced text transformations. Cons: More complex and harder to read. Slower and less efficient. Recommendations Use ${var^^} and ${var,,} if your script is Bash-specific and you want cleaner, faster code. Use tr if you need POSIX compliance or maximum portability. Use awk if you need complex transformations or additional string manipulation.
c - Case conversion with declare declare command is primarily used to declare variables and assign attributes to them... such as making them read-only, integer-typed, or modifying their case automatically. While declare is not directly used for case conversion it does support two options... that can be used to automatically enforce case on the values of variables. declare -l var → Forces the variable var to always store its value in lowercase. declare -u var → Forces the variable var to always store its value in uppercase. Limitations: Not POSIX-compliant, these features are specific to Bash No string-level case conversion No support for mixed case enforcement Only works on variable assignment, not on command outputs or arbitrary string processing.