Bash - Clearing the last output correctly

Question

I\'m trying to create an update-able progress status. In order to do that, I need to be able to clear the last output in its entirety so that I can update it. Carriage retur

Answer 1

Something tricky

Inspired by How to get the cursor position in bash?

#!/bin/bash

lineformat="This is a very long line with a lot of stuff so they will take " 
lineformat+="more than standard terminal width (80) columns... Progress %3d%%" 

n=0
while [[ $n -ne 100 ]]; do
    n=$((n+1))
    printf -v outputstring "$lineformat" $n
    twidth=$(tput cols)      # Get terminal width
    theight=$(tput lines)    # Get terminal height
    oldstty=$(stty -g)       # Save stty settings
    stty raw -echo min 0     # Suppres echo on terminal
    # echo -en "\E[6n"
    tput u7                  # Inquire for cursor position
    read -sdR CURPOS         # Read cursor position
    stty $oldstty            # Restore stty settings
    IFS=\; read cv ch <<<"${CURPOS#$'\e['}" # split $CURPOS
    uplines=$(((${#outputstring}/twidth)+cv-theight))
    ((uplines>0)) &&
        tput cuu $uplines    # cursor up one or more lines
    tput ed                  # clear to end of screen
    tput sc                  # save cursor position
    echo -n "$outputstring"
    tput rc                  # restore cursor
    sleep .0331s
done
echo

As tput cols and tput lines is initiated at each loop, you could resize window while running, cuu argument will be re-computed.

More complex sample

• Using trap WINCH for querying terminal size only when window is resized
• Addind newlines for scrolling up before cuu
• Reducing forks to tput

There:

#!/bin/bash

lineformat="This is a very long line with a lot of stuff so they will take " 
lineformat+="more than standard terminal width (80) columns... Progress %3d%%" 

getWinSize() {
    {
        read twidth
        read theight
    } < <(
        tput -S - <<<$'cols\nlines'
    )
}
trap getWinSize WINCH
getWinSize

getCpos=$(tput u7)
getCurPos() {
    stty raw -echo min 0
    echo -en "$getCpos"
    read -sdR CURPOS
    stty $oldstty
    IFS=\; read curv curh <<<"${CURPOS#$'\e['}"
}
oldstty=$(stty -g)

before=$(tput -S - <<<$'ed\nsc')
after=$(tput rc)
n=0
while [[ $n -ne 100 ]]; do
    n=$((n+1))
    printf -v outputstring "$lineformat" $n
    getCurPos
    uplines=$(((${#outputstring}/twidth)+curv-theight))
    if ((uplines>0)) ;then
        printf -v movedown "%${uplines}s" ''
        echo -en "${movedown// /\\n}"
        tput cuu $uplines
    fi
    printf "%s%s%s" "$before" "$outputstring" "$after"
    sleep .05
done

downlines=$((${#outputstring}/twidth))
printf -v movedown "%${downlines}s" ''
echo "${movedown// /$'\n'}"