linux学习之shell脚本 ------- 控制流结构

[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
  注:if语句必须以fi终止。

  如果没有condition2,则if语句可以简化为如下:

if condition
then 
      command1
else
       command2
fi
或:

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

  给予可执行权限,执行该脚本:

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
  注意,其中用于了比较运算符,更加详细的比较运算符,请参考man test。


  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
  运行结果:

jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./for_test1.sh 
1
2
3
4
5
for_test2.sh

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

jesson@jesson-K43SV:~/develop/worksapce/shell_workspace$ ./for_test2.sh 
orange
red
blue
gray
for_test3.sh

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

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
  给予权限,执行结果如下:

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
  给予权限,执行:

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
while_test2.sh

#!/bin/bash
#while_test
while read NAME
do
   echo $NAME
done <name.txt
  给予权限,执行:

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
   给予权限,执行如下:

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

continue_test.sh

#!/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
  同样,给予可执行权限,执行

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

 



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