feh wallpapers setting loop

wallpapers.sh

#!/bin/bash
d=$1 # Directory
t=$2 # Duration

if [ "$1" == "" ];then
    d=~/Pictures/Cities
fi
if [ "$2" == "" ];then
    t=300 # 5 minuts
fi

l=$(ls -1q "$d" | wc -l) # number of files

while true
do
    rindex=$[ $RANDOM % "$l" ] # start from random position
    counter=1
    for i in $(ls "$d")
    do
	img="$d/$i"
	if [ -f $img ] && [ $counter -gt $rindex ];then
	    feh --bg-scale $img
	    # echo $img
	    sleep "$t"s
	fi
	counter=$(($counter + 1))	
    done
done