# Array with expressions

expressions=("Ploink Poink" "I Need Oil" "Some Bytes are Missing!" "Poink Poink" "Piiiip Beeeep!!" "Hello" "Whoops! I'm out of memmory!")

# Seed random generator

RANDOM=$$$(date +%s)

# Loop loop loop loop loop loop ...

while [ 1 ]

do

    # Get random expression...

    selectedexpression=${expressions[$RANDOM % ${#expressions[@]} ]}

    # Write to Shell

    echo $selectedexpression

    # Wait an half hour

    sleep 1 # It's one second for debugging, dear SOers

done