What I'd like to do is take, as an input to a function, a line that may include quotes (single or double) and echo that line exactly as it was provided to the function. For instance:

function doit {
   printf "%s " ${@} 
   eval "${@}"
   printf " # [%3d]\n" ${?}
}

Which, given the following input

doit VAR=42
doit echo 'single quote $VAR'
doit echo "double quote $VAR"

Yields the following:

VAR=42  # [  0]
echo single quote $VAR  # [  0]
echo double quote 42  # [  0]

So the semantics of the variable expansion are preserved as I'd expect, but I can not get the exact format of the line as it was provided to the function. What I'd like is to have doit echo 'single quote $VAR' result in echo 'single quote $VAR'.

I'm sure this has to do with bash processing the arguments before they are passed to the function; I'm just looking for a way around that (if possible).

Edit

So what I had intended was to shadow the execution of a script while providing an exact replica of the execution that could be used as a diagnostic tool including exit status of each step.

While I can get the desired behavior described above by doing something like

while read line ; do 
   doit ${line}
done < ${INPUT}

That approach fails in the face of control structures (i.e. if, while, etc). I thought about using set -x but that has it's limitations as well: " becomes ' and exit status is not visible for commands that fail.