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Control cursor position also at bottom of window


 
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# 1  
Old 02-03-2020
Control cursor position also at bottom of window

I have a slight problem controlling the cursor position in a Bash terminal window. I have a function ask a question and then wait for an answer which is either 'y' or 'n' or a carriage return. Whenever the user enters anything else it just erases the answer and waits for the next one. However, the script behaves differently when the cursor is on the bottom line of a window as compared to any other line.
Code:
#!/bin/bash

# -----
# function: askYesOrNo
# purpose : ask question passed as $1
# return  : 0 if answer was y or Y, 
#           1 otherwise
# -----
function askYesOrNo {
        printf "\e[1;31;47m$1 [Y|n]\e[0m "      # print $1 in color
        printf "\e[s"                           # save cursor x-pos

        while true ; do
                read answer
                if [ -z "$answer" ] ; then
                        return 0
                elif [ "$(tr -d "NnYy" <<< $answer)" != "$answer" ] ; then
                        break
                fi
                # restore cursor x-pos, erase rest of line
#               printf "\e[u\e[K"     
                # restore cursor x-pos, erase rest of line
                printf "\e[u\e[1A\e[K"      
        done
        if [ "${answer^}" == "Y" ]; then
                return 0
        fi
        return 1
}


for (( i = 100, max = 110; i <= max; i++ )) ; do
        printf " %d\n" $i
        if [ $i -eq $max ] ; then
                if askYesOrNo "Do you wish to continue?" ; then
                        (( max += 10 ))
                fi
        fi
done

The for-loop is the 'productive' part. It just puts out numbers in a column. Every 10 numbers it asks if the user wants to continue and uses the function askYesOrNo for that purpose.

The problem lies with the two lines in the function askYesOrNo (at the end of the while-loop) and when the user enters an answer that is not Y, y, N, n or Enter. The first line (now commented out) works fine when the cursor is not in the bottom line of the window. But if it is then the window scrolls up and the next answer appears in the next line.

The second version moves the cursor one line up and that's fine with the cursor at the bottom of the window but not if the question is asked elsewhere.

How can I get this to work in every situation?
# 2  
Old 02-03-2020
Hi Ralph...

Some terminals don't always follow terminal escape codes to the _letter_.
You could try and force the line prompt, force the cursor to the correct position and force clearing after the line prompt.
An example of the cursor forcing, it is just as easy to manipulate this to write the prompt and clear the line
Code:
printf "\033[12;36fSome prompt: \n"

# 3  
Old 02-03-2020
But how do I know the correct position? It keeps changing as the script proceeds.
# 4  
Old 02-03-2020
Would a (man console_codes)
Code:
ESC M     RI       Reverse linefeed.

help?
# 5  
Old 02-03-2020
An example clearing the screen/window:
Code:
while true
do
        printf "\033[2J\033[H\033[12;30fSome prompt: "
        read -r text
done

EDIT:

You can omit the \033[H if you wish but some terminals will not clear correctly without it...

Last edited by wisecracker; 02-03-2020 at 08:01 PM.. Reason: see EDIT:
# 6  
Old 02-03-2020
Quote:
Originally Posted by RudiC
Would a (man console_codes)
Code:
ESC M     RI       Reverse linefeed.

help?
Cool manual page but no... the page still scrolled up and I ended up in the next line, rather than restarting in the same line.

I think I have to check whether the cursor is in the last line of the window or not and do the reverse line feed only in that case. Together with an answer that I found elsewhere on this forum I came up with this version of the function which apparently works now:

Code:
function askYesOrNo {
        printf "\e[1;31;47m$1 [Y|n]\e[0m "      # print $1 in color
        printf "\e[s"                           # save cursor x-pos
    
        while true ; do
                read answer
                if [ -z "$answer" ] ; then
                        return 0
                elif [ "$(tr -d "NnYy" <<< $answer)" != "$answer" ] ; then
                        break
                fi

                # How many lines in this window?
                LINES=$(tput lines)

                # find cursor y-position ( line number )
                printf "\e[6n" ; read -sd R POS 
                CURPOS=${POS#*[}; CUR_Y=${CURPOS%;*}
 
                if [ "$CUR_Y" -eq "$LINES" ] ; then
#                       printf "\e[u\e[1A\e[K" 
                        printf "\e[u\eM\e[K"
                else
                        printf "\e[u\e[K" 
                fi                          
        done
        if [ "${answer^}" == "Y" ]; then 
                return 0
        fi  
        return 1
}

# 7  
Old 02-03-2020
Same idea here, but also using CSI sequence



Code:
      r   DECSTBM   Set scrolling region; parameters are top and bottom row.



to reduce that region to last line. Not yet the ultimate answer, but worth a try, mayhap.



Code:
function askYesOrNo     { read -sdR -p $'\e[6n' TMP
                          TMP="${TMP#??}"
                          [ "${TMP%;*}" -eq "$LINES" ] && printf "\e7\e[$LINES;120r\e8"
                          while true 
                            do  read -p$'\e[1;31;47m'"$1 [Y|n]"$'\e[0m \e[s' answer
                                answer=${answer:-Y}
                                answer=${answer^^}
                                [ "${answer//[YN]}" = "${answer}" ] || break 
                            done
                          printf "\e7\e[1;${LINES}r\e8"
                          [ "$answer" = "Y" ] && return 0
                          return 1
                        }


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