Make "sudo apt-get update" output only what it is doing on one line

This will be difficult to do without writing a proper application that uses ncurses or similar to control the terminal. With bash, you can get some of this effect with the following script:

#! /bin/bash
height=${1:-5}

# Buffer up to the height
do_height()
{
    for ((i = 0; i < height; i++))
    do
        "$@"
    done
}

do_height printf "%-${cols}s\n" ""

# Get dimensions of terminal
cols=$(tput cols)
lines=$(tput lines)

sudo apt-get update |&
    while IFS= read -r line
    do 
        sleep 0.01
        if [[ $line =~ ^(Hit|Get|Fetch|Read) ]]
        then
            out=("$line" "${out[@]:0:4}")
        else
            out=("" "${out[@]:0:4}")
            tput cup $((lines - height - 1)) 0
            printf "%-${cols}s\n" "$line"
            do_height printf "%-${cols}s\n" ""
        fi
        tput cup $((lines - height - 1)) 0
        for ((i = height - 1; i >= 0; i--))
        do
            printf "%-${cols}s\n" "${out[i]}"
        done
    done

Run as foo.sh N where N is the number of lines you want to keep. Note that:

• this assumes you're at the bottom of the terminal.
• errors will always be printed N lines above the last line.
• apt-get provides more transient output when it's printing to a terminal, so the output here will seem jerky as intermediate lines are not available.

So the final output will look like: