问题
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 $(whoami)
I realize this can be done with tr, sed, awk, printf, cut, etc.; but that is not the point of the question.
Any help is appreciate!
This isn't the real code or anything indicative of what I am wanting to actually do. I will often default (or try to) to using just one command over concatenating multiple commands.
I've seen other posts state that concatenating within the braces are not possible, but I know that everything is possible.
Please don't:
- Reference other posts as duplicate that say it's impossible
回答1:
One liner:
sVar=$(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.)
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:
…
- Each variable assignment shall be expanded for tilde expansion, parameter expansion, command substitution, arithmetic expansion, and quote removal prior to assigning the value.
来源：https://stackoverflow.com/questions/37257993/combining-multiple-bash-parameter-substitutions-within-same-variable-set-line-wi