Bash completion with changing number?

Question

I would like to create a function or alias or command completion in bash which would take a command as "dfk-1234" or "DFK-nnnnn" (the number can be 1 to 5 digits, not zero-padded), and run a command "dfkp DFK-nnnn".

Arguments should be passed through verbatim. "dfk-18875 cat file.txt" should become "dfpk DFK-18875 cat file.txt".

I think command completion or tab expansion would work, but can't figure how to do it when the number changes.

What's the best way to do this? Once I can handle the main command name, then I can handle the rest (case, arguments, etc).

Answer 1

Bash 4.0 introduced new functionality for handling commands that are not found -- it will call a function named command_not_found_handle, if that function exists. You could use that behavior to intercept calls to "programs" named dfk-NNN or DFK-NNN and re-run them as you like. Since we're depending on 4.0 behavior already, I've used the upper-casing and lower-casing parameter expansion features as well.

command_not_found_handle() {
  case "${1,,}" in
        (dfk-?|dfk-??|dfk-???|dfk-????|dfk-?????)
                echo dfkp "${1^^}" "${@:2}"
                return 0
        ;;
        (*)
                printf 'bash: %s: command not found\n' "$1" >&2
                return 127
        ;;

  esac
}

If you enter a command that doesn't exist, bash calls this function with the original command-line. The case statement lower-cases the first argument so that it's simpler to compare it against the dfk patterns required.

If the command starts with dfk- and ends with 1, 2, 3, 4, or 5 characters (tighten this to be digits as you see fit), then it -- currently echos, for debugging, but then -- calls the dfkp program with the first parameter being the upper-cased version of the initial dfk entry, followed by the remainder of the command-line.

For commands that don't match dfk-NNNN, it falls through and prints a simulated bash error message to stderr and returns 127. (This matches the default behavior, as if command_not_found_handle did not exist).

A sample session (with the echo debugging installed, as I don't have an actual dfkp program):

$ dfk-1234
dfkp DFK-1234
$ dfk-18875 cat file.txt
dfkp DFK-18875 cat file.txt
$ some-other-command
bash: some-other-command: command not found
$ dfk-1
dfkp DFK-1
$ dfk-12345
dfkp DFK-12345