This may sound silly, but it works:   print STDERR the actual string that you intend to execute, then copy/paste that literal string to a new terminal session and try it.   Inevitably, you will right-away discover one of two things:   that the string isn’t as you thought it would be, or that when run by an actual shell it produces a syntax error of some kind.   So, avoid guessing ... try it.   (No one will see you say, “d’oh!”)