[本文是自己学习所做笔记，欢迎转载，但请注明出处：http://blog.csdn.net/jesson20121020]

今天开始学一些同其他高级语言一样的shell流控制结构

流控制语句：

　　1. if语句

　　　语句格式：　　　　

if condition1      
then
   command1
else condition2
then
   command2
else
   command3
fi

　　如果没有condition２,则if语句可以简化为如下：

if condition
then 
      command1
else
       command2
fi

if condition
then 
      command1
fi

　　　例子：

if_test.sh

#!/bin/bash
#if_test
echo -n "please input two number(a and b):"
read a b
if [ $a -lt $b ]
then
   echo "$a is less than $b"
elif [ $a -gt $b ]
then
   echo "$a is greater than $b"
else
   echo "$a ia equal to $b"
fi

jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ chmod a+rx if_test.sh
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./if_test.sh 
please input two number(a and b):10 10
10 ia equal to 10
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./if_test.sh 
please input two number(a and b):10 12
10 is less than 12
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./if_test.sh 
please input two number(a and b):8 2
8 is greater than 2

　　2. case语句

　　　语句格式：

　　　　case value in

　　　　模式１)

　　　　　　command1

　　　　　　;;

　　　　模式２)

　　　　　　command2

　　　　　　;;

　　　　esac

　　　注意：

　　　　１case取值后面必须为单词in，每一模式必须以右括号结束，取值可以为变量或者常数。

　　　　 2 模式匹配符*表示任意字符；?表示任意单字符；[...]表示类或范围中任意字符。

　　　例子：

case_test.sh

#!/bin/bash
#case_test
echo -n "Enter a number from 1 to 3:"
read n
case $n in
1)
    echo "You select 1"
    ;;
2)
    echo "You select 2"
    ;;
3)
    echo "You select 3"
    ;;
*)  echo "You select *"
    ;;
esac

jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ chmod a+rx case_test.sh 
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./case_test.sh 
Enter a number from 1 to 3:1
You select 1
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./case_test.sh 
Enter a number from 1 to 3:2
You select 2
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./case_test.sh 
Enter a number from 1 to 3:3
You select 3
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./case_test.sh 
Enter a number from 1 to 3:*
You select *
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./case_test.sh 
Enter a number from 1 to 3:20
You select *

　　3. for循环

　　　格式：

　　　　for 变量名 in 列表

　　　　do

　　　　　命令１

　　　　　命令２

　　　　done

　　　例子：

for_test1.sh

#!/bin/bash
#for_test
for loop in 1 2 3 4 5
do
    echo $loop
done

jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./for_test1.sh 
1
2
3
4
5

#!/bin/bash
#for_test2
for loop in orange red blue gray
do
   echo $loop
done

jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./for_test2.sh 
orange
red
blue
gray

#!/bin/bash
#for_test3
for loop in `cat name.txt`
do
    echo $loop
done

jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ cat name.txt 
jesson
cherry
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./for_test3.sh 
jesson
cherry

　　4. until循环

　　　格式：

　　　　until　条件

　　　　do

　　　　　　命令

　　　　done

until_test.sh

#!/bin/bash
#until_test
i=10
until [ $i -lt 0 ]
do
    echo $i
    let i=i-1
   # ((i=$i-1))
   #i=$[i-1]
done

jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ chmod a+rx until_test.sh 
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./until_test.sh 
10
9
8
7
6
5
4
3
2
1
0

　　5. while循环

　　　格式：

　　　　while　命令

　　　　do

　　　　　 　命令

　　　　　　.......

　　　　done

　　　例子：

while_test1.sh

#!/bin/bash
#while_test1
while echo -n "输入你喜欢的明星:";read Mingxing
do
    echo "$Mingxing 是你喜欢的明星"
done

jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ chmod a+rx while_test1.sh 
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./while_test1.sh 
输入你喜欢的明星:周杰
周杰 是你喜欢的明星
输入你喜欢的明星:孙楠
孙楠 是你喜欢的明星

#!/bin/bash
#while_test
while read NAME
do
   echo $NAME
done <name.txt

jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ chmod a+rx while_test2.sh 
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./while_test2.sh 
jesson
cherry

　　6. break和continue

　　　break [n]

　　　－退出循环

　　　－如果是在一个嵌入循环里，可以指定n来跳出的循环个数。

　　　continue

　　　－跳过循环步

　　　注意，这和其他高级语言中的一样，continue命令类似于break，只有一点差别，它不会跳出循环，而是路过当前循环步。

　　　例子：

break_test.sh

#!/bin/bash
#break_test.sh
while :
do
    echo -n "Enter any number(1,...,5):"
    read ANS
    case $ANS in
    1|2|3|4|5)
        echo "You enter anumber between 1 and 5"
        ;;
    *)
        echo "Wrong number,Bye"
        break;
        ;;
    esac
done

jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ chmod a+rx break_test.sh 
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./break_test.sh 
Enter any number(1,...,5):1
You enter anumber between 1 and 5
Enter any number(1,...,5):2
You enter anumber between 1 and 5
Enter any number(1,...,5):3
You enter anumber between 1 and 5
Enter any number(1,...,5):4
You enter anumber between 1 and 5
Enter any number(1,...,5):5
You enter anumber between 1 and 5
Enter any number(1,...,5):6
Wrong number,Bye

#!/bin/bash
#continue_break_test
while :
do
     echo -n "Enter any number(1,...,5):"
     read ANS
     case $ANS in
     1|2|3|4|5)
         echo "You enter a number between 1 and 5"
         ;;
     *)
         echo -n "Wrong number,continue(y/n)?:"
         read IS_CONTINUE
         case $IS_CONTINUE in
         y|yes|Y|Yes)
                continue
                ;;
         *)
                break
                ;;
         esac
     esac
done

jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ chmod a+rx continue_test.sh 
jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./continue_test.sh 
Enter any number(1,...,5):2
You enter a number between 1 and 5
Enter any number(1,...,5):3
You enter a number between 1 and 5
Enter any number(1,...,5):4
You enter a number between 1 and 5
Enter any number(1,...,5):5
You enter a number between 1 and 5
Enter any number(1,...,5):8
Wrong number,continue(y/n)?:y
Enter any number(1,...,5):1
You enter a number between 1 and 5
Enter any number(1,...,5):79
Wrong number,continue(y/n)?:n

linux学习之shell脚本 ------- 控制流结构