Условия if

if [ condition ]
then
    command
elif [ condition ]
then
    command
else
    command
fi

Логические операторы в условиях

if [ $condition1 ] && [ $condition2 ] ...
if [[ $condition1 && $condition2 ]] ...

Ветвления case

case ABC in
condition1)
  command
;;
condition2)
  command
;;
esac