Change wallpaper

change_wallpaper.sh

#!/bin/bash

# change me
root="$HOME/pics/wallpaper"

# dependency
command -v feh >/dev/null 2>&1 || { echo >&2 "$0 error: missing dependency (\"feh\")"; exit 1; }

# reason for this here: http://yhaupenthal.org/1265597121.htm
export DISPLAY=:0.0

# get the resolution of all monitors together
res=$(xrandr | head -1 |  tr -d ' ' | cut -d\, -f 2 | sed 's/current//')
src="$root/$res"
if [[ ! -d "$src" ]] ; then
        echo >&2 "$0 error: no such folder (\"$src\")"
        exit 1
else
        # how many files in $src
        lines=$(ls "$src" | wc -l)
        # get a random number
        rand=$(shuf -i 1-"$lines" -n 1)
        # get the pic belonging to the number
        pic=$(ls "$src" | sed -n "${rand}p")

        # show it with feh
        feh --bg-tile "$src/$pic"
fi