Cursor Backward (CUB)

The parameter n must be an integer greater than or equal to 1. If n is less than or equal to 0, adjust n to be 1. If n is omitted, n defaults to 1.

This sequence always unsets the pending wrap state.

The leftmost boundary the cursor can move to is determined by the current cursor column and the left margin. If the cursor begins to the left of the left margin, modify the left margin to be the leftmost column for the duration of the sequence. The leftmost column the cursor can be on is the left margin.

With the above in place, there are three different cursor backward behaviors depending on the mode state of the terminal. The possible behaviors are listed below. In the case of a conflict, the top-most behavior takes priority.

• Extended reverse wrap: wraparound (mode 7) and extended reverse wrap (mode 1045) are BOTH enabled
• Reverse wrap: wraparound (mode 7) and reverse wrap (mode 45) are BOTH enabled
• No wrap: The default behavior if the above wrapping behaviors do not have their conditions met.

For the no wrap behavior, move the cursor to the left n cells while respecting the aforementioned leftmost boundary. Upon reaching the leftmost boundary, stop moving the cursor left regardless of the remaining value of n. The cursor row remains unchanged.

For the extended reverse wrap behavior, move the cursor to the left n cells while respecting the aforementioned leftmost boundary. Upon reaching the leftmost boundary, if n > 0 then move the cursor to the right margin of the line above the cursor. If the cursor is already on the top margin, move the cursor to the right margin of the bottom margin. Both the cursor column and row can change in this mode. Compared to non-extended reverse wrap, the two critical differences are that extended reverse wrap doesn't require the previous line to be wrapped and extended reverse wrap will wrap around to the bottom margin.

For the reverse wrap (non-extended) behavior, move the cursor to the left n cells while respecting the aforementioned leftmost boundary. Upon reaching the leftmost boundary, if n > 0 and the previous line was wrapped, then move the cursor to the right margin of the line above the cursor. If the previous line was not wrapped, the cursor left operation is complete even if there is a remaining value of n. If the cursor is already on the top margin, do not move the cursor up. This wrapping mode does not wrap the cursor row back to the bottom margin.

For extended reverse wrap or reverse wrap modes, if the pending wrap state is set, decrease n by 1. In these modes, the initial cursor backward count is consumed by the pending wrap state, as if you pressed "backspace" on an empty newline and the cursor moved back to the previous line.

cols=$(tput cols)
printf "\033[${cols}G" # move to last column
printf "A" # set pending wrap state
printf "\033[D" # move back one
printf "XYZ"

|________XY|
|Zc________|

printf "\033[?45l" # disable reverse wrap
echo "A"
printf "\033[10D" # back
printf "B"

|A_________|
|Bc________|

cols=$(tput cols)
printf "\033[?7h" # enable wraparound
printf "\033[?45h" # enable reverse wrap
printf "\033[1;1H" # move to top-left
printf "\033[0J" # clear screen
printf "\033[${cols}G" # move to end of line
printf "AB" # write and wrap
printf "\033[D" # move back two
printf "X"

|_________Xc
|B_________|

printf "\033[?7h" # enable wraparound
printf "\033[?1045h" # enable extended reverse wrap
printf "\033[1;1H" # move to top-left
printf "\033[0J" # clear screen
echo "A"
printf "B"
printf "\033[2D" # move back two
printf "X"

|A________Xc
|B_________|

cols=$(tput cols)
printf "\033[?7h" # enable wraparound
printf "\033[?1045h" # enable extended reverse wrap
printf "\033[1;1H" # move to top-left
printf "\033[0J" # clear screen
printf "\033[1;3r" # set scrolling region
echo "A"
printf "B"
printf "\033[D" # move back one
printf "\033[${cols}D" # move back entire width
printf "\033[D" # move back one
printf "X"

|A_________|
|B_________|
|_________Xc

printf "\033[1;1H"
printf "\033[0J"
printf "\033[?45h"
printf "\033[3r"
printf "\b"
printf "X"

|__________|
|__________|
|Xc________|

cols=$(tput cols)
printf "\033[?45h"
printf "\033[${cols}G"
printf "\033[4D"
printf "ABCDE"
printf "\033[D"
printf "X"

|_____ABCDX|