Command line tools in 10 lines of ruby (using this script):

    docker ps | rb drop 1 | rb -l split[1]
    docker ps -a | rb grep /Exited/ | rb -l 'split.last.ljust(20) + " => " + split(/ {2,}/)[-2]'
    df -h | rb 'drop(1).sort_by { |l| l.split[-2].to_f }'

Command line tools in zero lines of ruby (using ruby):

    docker ps | ruby -lane 'next if $. == 1; print $F[1]
    docker ps -a | ruby -lne 'print $1 if /(Exited .*? ago)/'
    df | ruby -lane 'BEGIN { lines = [] }; lines.push [$F[4].to_i, $_] if $. > 0; END { lines.sort { |a,b|b[0] <=> a[0] }.each{|k| print k[1] } }

Bit of a pain as ++ is lacking, as is autovivication. a /bin/sort at the end usually beats `<=>` for terseness.