Shell Programming and Scripting

#!/bin/bash
validateTimeFormat()
{
checkTime=$1
timePattern="[0-2][0-9]:[0-5][0-9]:[0-5][0-9]"
if [[ $checkDate =~ $timePattern ]]
then
echo "Valid time pattern"
return 1
else
echo "InValid time pattern"
return -1
fi
}
echo "Please enter the end time [hh:mm:ss]"
read END_TIME
echo "Time entered is $END_TIME"
validateTimeFormat $END_TIME
if [ $? -ne "1" ];
then
echo "Time format entered is wrong"
exit 0
fi

validateTimeFormat()
{
  if date -d "$1" >/dev/null # you can enventually remove redirection...
  then
    echo "Valid time pattern"
    return 0
  else
    echo "InValid time pattern"
    return 1
  fi
}

date -d "$1" >/dev/null
# which returns 0 (true if OK)