1、单分支语句

if [ ];then
    命令
fi

if [ ]
then
    命令
fi

2、双分支语句

if [ ]
then
    echo cmd1
else
    echo cmd2
fi

3、多分支语句

if condition1
 
then
    command1
 
elif condition2
 
then
    command2
 
else
 
    commandN
 
fi