bash control characters explained

#!/usr/bin/env bash
# Thank you, Lee Maschmeyer, for this example.
read -n 1 -s -p \
$'Control-M leaves cursor at beginning of this line. Press Enter. \x0d'
 # Of course, '0d' is the hex equivalent of Control-M.
echo >&2 # The '-s' makes anything typed silent,
 #+ so it is necessary to go to new line explicitly.
read -n 1 -s -p $'Control-J leaves cursor on next line. \x0a'
 # '0a' is the hex equivalent of Control-J, linefeed.
echo >&2
###
read -n 1 -s -p $'And Control-K\x0bgoes straight down.'
echo >&2 # Control-K is vertical tab.
# A better example of the effect of a vertical tab is:
var=$'\x0aThis is the bottom line\x0bThis is the top line\x0a'
echo "$var"
# This works the same way as the above example. However:
echo "$var" | col
# This causes the right end of the line to be higher than the left end.
# It also explains why we started and ended with a line feed --
#+ to avoid a garbled screen.
# As Lee Maschmeyer explains:
# --------------------------
# In the [first vertical tab example] . . . the vertical tab
#+ makes the printing go straight down without a carriage return.
# This is true only on devices, such as the Linux console,
#+ that can't go "backward."
# The real purpose of VT is to go straight UP, not down.

from advanced bash scripting guide