a='▂▄▆█'; s=$(iwconfig wlp61s0 | sed -E-n 's/[^0-9]=([0-9]{1,})/70.$/\1/p') ; : ${s:='-18'}; echo ${a:0:$(( ( $s / 18 ) + 1 ))}

call to spark is useless and code is unsightly (even for bash)

furthermore, sparks 0 1 2 3 4, and spark 1 2 3 4 0, differs from spark 1 2 3 4