Пример условных операторов на bash

#!/bin/bash

dat=`date +%H`
morning=12
afternoon=15
evening=24

if [ $dat -le $morning ] 
then
        echo "Good morning sir" |festival --tts

elif [ $dat -gt $morning ] && [ $dat -le $afternoon ]
then
        echo "Good afternoon sir"|festival --tts

elif [ $dat -gt $afternoon ] && [ $dat -le $evening ]
then
        echo "Good evening sir"|festival --tts
fi