$ printf "abc" > some-file
$ cat some-file
abc$

# injects the arguments into the terminal, from the second link
function inject() {
  perl -e 'ioctl(STDIN, 0x5412, $_) for split "", join " ", @ARGV' "$@"
}
# prints a newline if the cursor is not in position 1
clear_newline() {
  local curpos # local variable to hold the cursor position
  local input  # local variable to hold entered input
  stty -echo # disable echoing
inject '
' # inject a newline to terminate entered input, '' didn't work?
  IFS='n' read -s input # read entered input
  echo -en '33[6n'
  # ask the terminal driver to print the current cursor position
  IFS=';' read -d R -a curpos # read cursor position
  stty echo # enable echoing
  (( curpos[1] > 1 )) && echo -e '33[7m%33[0m'
  # if cursor not in first column, print a % with inverted colours and a newline
  stty -echo # disable echoing of input to terminal again
  inject "${input}" # inject stored input
  stty echo # enable echo
}

PROMPT_COMMAND='clear_newline' # run clear_newline for every prompt