Select statement: if, case, select.
Loop statement: for, while, until.
Note: The following variables are named var
Forward + reverse structure: if, case
if format:
if Conditional judgment
then
content
elif
then
content
else
content
be
case format:
case $ var in
1) ...;;
2) ...;;
...
*) ...;;
esac
do + done结构：for,while,until,select
for format:
for var in list
do
content
done
while format:
while conditional judgment -----" If true, enter the loop
do
content
done
until format:
until conditional judgment -----" If false, enter the loop
do
content
done
select format:
select var in list
do
break
done