Execute command containing quotes from shell variable [duplicate]

Question

I'm currently having problems to execute a command from a shell variable.

In general the following works as expected:

COMMAND="echo A" echo $COMMAND $COMMAND 

produces:

echo A A 

But if I do

COMMAND="su aUser -s /bin/bash -c 'echo A'" echo $COMMAND $COMMAND 

I get

su aUser -s /bin/bash -c 'echo A' Password:  A': -c: line 0: unexpected EOF while looking for matching `'' A': -c: line 1: syntax error: unexpected end of file 

If I enter the line

su aUser -s /bin/bash -c 'echo A' 

directly it works as expected.

It seems my assumption that $COMMAND is equal to entering the content as command directly is wrong.

Questions

1) Does anyone know how I can run the command from a variable?

2) What exactly is the difference between

COMMAND="command" $COMMAND 

and

command 

?

Answer 1

Arrays are useful to keep your parameters whole:

command=(su aUser -s /bin/bash -c 'echo A') 

and invoke it exactly like this:

"${command[@]}"