Combining multiple bash parameter substitutions within same variable set line without using any other commands [closed]

Question

Example of what I want to combine:

sVar=$(whoami)
sVar=${sVar^}
sVar=${sVar::1}

Output:

• Uppercase first character of username

Requirements:

• One-liner
• Do the rest of the processing with parameter substitutions except for the initial command substitution above $(whoami)

I realize this can be done with tr, sed, awk, printf, cut, etc.; but that is not the point of the question.

Any help is appreciate!

This isn't the real code or anything indicative of what I am wanting to actually do. I will often default (or try to) to using just one command over concatenating multiple commands.

I've seen other posts state that concatenating within the braces are not possible, but I know that everything is possible.

Please don't:

• Reference other posts as duplicate that say it's impossible

Answer 1

One liner:

sVar=$(whoami) sVar=${sVar^} sVar=${sVar::1}

It may not be what you were looking for, but it is certainly a single command and uses parameter substitutions. A single command can consist of multiple variable assignments, in which case they are performed left to right.

The subject of a parameter substitution is a variable name, an indirection (a ! followed by a variable name), or a subscript expression (a variable name -- not an indirection -- followed by a subscript within [ and ]. That's a bit limited, to be sure, but that's bash. (Posix shell is even more restrictive; it has no indirection nor arrays, and fewer types of expansion.)

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Posix wording from XCU, emphasis added:

When a given simple command is required to be executed… the following expansions, assignments, and redirections shall all be performed from the beginning of the command text to the end:

…

4. Each variable assignment shall be expanded for tilde expansion, parameter expansion, command substitution, arithmetic expansion, and quote removal prior to assigning the value.