目录
前言
一、if-else
二、for循环
三、while语句、无限循环和until循环
1.while语句
2.无限循环
3.until循环
四、case ... esac
五、跳出循环
1.break
2.continue循环
总结
前言
Shell流程控制包括：if-else语句、for循环、while语句、无限循环、until循环、case ... esac和跳出循环。
一、if-else
- if结构的几种写法
# if 控制语句# if判断
# if command;
# then
# code
# fi# if else 语句
# if command;
# then
# code
# else
# code
# fi# if elif else 语句
# if command;
# then
# code
# elif command2;
# then
# code
# *n
# else
# code
# fi- 举例：
#!/bin/shif [ `ps -ef | grep -c "ssh"` -gt 1 ]; # ps -ef 列出当前系统中所有的进程信息。# grep -c "ssh" 统计这些进程信息中包含字符串 "ssh" 的行数。
thenecho "True"
fiecho "-----------------"
if ((10>29));
then echo "10 bigger then 20"
elseecho "10 less then 20"
fiecho "------------------"
# elif
a=10
b=20
if [ $a -eq $b ];
then echo "a=b"
elif [ $a -gt $b ];
thenecho "a>b"
else [ $a -lt $b ];echo "a<b"
fi
- 输出：
True
-----------------
10 less then 20
------------------
a<b
二、for循环
- 结构：
# for循环
# for i in xxx;
# do
# code
# done- 举例：
#!/bin/shfor i in "I\'m good at coding";
do echo $i
donefor i in 1 2 3 4 5 ;
do echo the value is $i
donefor i in "$@"; # 文件传参 $@ 循环获取传入的参数
do echo $i
done- 输出：
[root@tokyo001 shell_code]# sh demo10.sh 2 3 4 5 5 # 文件传参写法
I\'m good at coding
the value is 1
the value is 2
the value is 3
the value is 4
the value is 5
2
3
4
5
5
三、while语句、无限循环和until循环
1.while语句
- 结构：
# while循环
# while codition
# do
# code
# done
- 举例：注意这里出现了shell编程里的自增语句 let "n++"
#!/bin/sha=1
while [ $a -le 5 ]
do echo $alet "a++" # 等价于 a=`expr $a + 1 `
done- 输出：
1
2
3
4
5
2.无限循环
- 结构：
#无限循环语法格式
# while : # 或者 while True
# do
# echo "im handsome"
# done# for ((;;))- 举例：
#!/bin/sh# 死循环
echo "请按ctrl+c结束"
echo -n "请输入你喜欢的电影：" # -n 不要在输出末尾添加换行符
while read film
do echo "${film}是一部好电影"
done- 输出：程序无限循环 按ctrl + c可退出
请按ctrl+c结束
请输入你喜欢的电影：hhh
hhh是一部好电影
xxxx
xxxx是一部好电影
gggg
gggg是一部好电影
3.until循环
- 举例：
#!/bin/sh# until循环 直到条件为真为止
a=0
until [ ! $a -lt 10 ]
do echo $alet "a++"
done
- 输出：
0
1
2
3
4
5
6
7
8
9
四、case ... esac
- 举例：
#!/bin/sh
# case esac 模式匹配echo "请输入1-4之间的数字"
read -p "请输入数字：" num
case $num in1)echo "you choose 1";; # 表示匹配结束2)echo "you choose 2";;3)echo "you choose 3";;4)echo "you choose 4";;*) # 8 通配其他结果echo "you choose others";;
esacecho "----------------"
a="hhh"
case $a in "hhh")echo "you are hhhhhhhhh";;"xxx")echo "you are xxxxxxxxx";;"ggg")echo "you are gggggggggg";;
esac
- 输出：一种是获取用户输入的数据进行判断，一种是直接判断
请输入1-4之间的数字
请输入数字：2
you choose 2
----------------
you are hhhhhhhhh
五、跳出循环
1.break
- break 命令允许跳出所有循环（终止执行后面的所有循环）
- 举例：
#!/bin/sh# break 跳出循环
echo "welcome to paris"
echo "plese tell me yuor age"
while :
do read -p "plese tell me yuor age of ten " agecase $age in1|2|3|4)echo "your are so yong";;*)echo "old man"break # 跳出整个循环;;esac
done- 输出：
welcome to paris
plese tell me yuor age
plese tell me yuor age of ten 1
your are so yong
plese tell me yuor age of ten 1
your are so yong
plese tell me yuor age of ten 1
your are so yong
plese tell me yuor age of ten 5
old man
2.continue循环
- continue 命令，仅跳出当前循环。
- 举例：
#!/bin/sh# continue 跳出循环
echo "welcome to paris"
echo "plese tell me yuor age"
while :
do read -p "plese tell me yuor age of ten " agecase $age in1|2|3|4)echo "your are so yong";;*)echo "old man"continue # 跳出当前循环;;esac
done- 输出：用户输入1,2,3,4以外的数字仍不会跳出整个循环，只跳出了这一次的循环
welcome to paris
plese tell me yuor age
plese tell me yuor age of ten 1
your are so yong
plese tell me yuor age of ten 2
your are so yong
plese tell me yuor age of ten 3
your are so yong
plese tell me yuor age of ten 1
your are so yong
plese tell me yuor age of ten 6
old man
plese tell me yuor age of ten 6
old man
plese tell me yuor age of ten
总结
Shell流程控制包括：if-else语句、for循环、while语句、无限循环、until循环、case ... esac和跳出循环。
Shell流程控制包括：if-else语句、for循环、while语句、无限循环、until循环、case ... esac和跳出循环。
重要的事情说三遍哈哈哈哈。
