prioritise iCloud syncing processes

sync.sh

#!/bin/sh
bird_pid=$(pgrep bird)
cloudd_pid=$(pgrep cloudd)
nsurlsessiond=$(pgrep nsurlsessiond)

# check all the values are not empty
# refactor to not use [[ ]] and use [ ] instead
if [[ -z "$bird_pid" || -z "$cloudd_pid" || -z "$nsurlsessiond" ]]; then
    echo "bird, cloudd or nsurlsessiond is not running"
    exit 1
fi

for pid in $bird_pid; do
    renice -n -10 -p "$pid"
done

for pid in $cloudd_pid; do
    renice -n -10 -p "$pid"
done

for pid in $nsurlsessiond; do
    renice -n -10 -p "$pid"
done