（各语法逻辑通用）

1、if语句

结构：

if   condition
then 
      statements
else
      statements
fi

2、elif语句（类似c语言中，else if）

二者样例：

#!/bin/sh
echo -n "Is it morning? Please answer yes or no "
read timeofday

if [ "$timeofday" = "yes" ]; then
	echo "Good morning"
elif [ "$timeofday" = "no" ]; then
	echo "Good afternoon"
else
	echo "Sorry,$timeofday not recognized. Enter yes or no "
	exit 1
fi
exit 0

结果：

Is it morning? Please answer yes or no yes
Good morning

3、if中判断条件注意：

其使用变量时，应该用“”标记。以免出现不合法问题。导致出现 ?：unary operator expected错误

4、for循环

结构：

for variable in values
do
    statements
done

样例

#!/bin/sh

for foo in "bar fud 43"
do
	echo $foo
done
exit 0

结果：

bar fud 43

5、while语句

结构：

while condition do
       statements
done

6、until语句（do…while)

结构：

until condition
do
       statements
done

样例：

#!/bin/sh

until who ? grep "$1" > /dev/null
do
	sleep 60
done
# now ring

echo -e '\a'
echo *****$1 has just logged in*****
exit 0

结果；

case1 case1~ first for hanshu if tiaojian try_var until useofbianliang has just logged in*****

7、case语句：

结构：

case variable in
      pattern [ ? pattern ] ... )   statement;;
      pattern [ ? pattern ]... )    statement;;
      ....
esac

样例：

#!/bin/sh

echo "Is it morning? Please answer yes or no"
read timeofday

case "$timeofday" in
	yes) echo "Good morning";;
	no ) echo "Good afternoon";;
	y  ) echo "Good Mornig";;
	n  ) echo "Good Afternoong";;
	*  ) echo "Sorry, answer not recognized";;
esac

exit 0

结果：

Is it morning? Please answer yes or no
yes
Good morning

8、其他：与或（&& ||）