http://www.fmi.uni-passau.de/archive/doc/unix/unixhelp/Unixhelp/commanz_cmd2.2.2.html (Einblicke ins Internet, 10/1995)\\ prevent the shell from expanding any single special character.
' ' prevent the shell from expanding all special characters enclosed
in this string except ! .
" " prevent the shell from expanding
any enclosed special character except $, ` and !.