bash script, erase previous line?

Question

In lots of Linux programs, like curl, wget, and anything with a progress meter, they have the bottom line constantly update, every certain amount of time. How do I do that in a

Answer 1

To actually erase previous lines, not just the current line, you can use the following bash functions:

# Clears the entire current line regardless of terminal size.
# See the magic by running:
# { sleep 1; clear_this_line ; }&
clear_this_line(){
        printf '\r'
        cols="$(tput cols)"
        for i in $(seq "$cols"); do
                printf ' '
        done
        printf '\r'
}

# Erases the amount of lines specified.
# Usage: erase_lines [AMOUNT]
# See the magic by running:
# { sleep 1; erase_lines 2; }&
erase_lines(){
        # Default line count to 1.
        test -z "$1" && lines="1" || lines="$1"

        # This is what we use to move the cursor to previous lines.
        UP='\033[1A'

        # Exit if erase count is zero.
        [ "$lines" = 0 ] && return

        # Erase.
        if [ "$lines" = 1 ]; then
                clear_this_line
        else
                lines=$((lines-1))
                clear_this_line
                for i in $(seq "$lines"); do
                        printf "$UP"
                        clear_this_line
                done
        fi
}

Now, simply call erase_lines 5 for example to clear the last 5 lines in the terminal.