第八章 shell學習之迴圈和結構化命令

標籤：迴圈 結構化命令 shell

for迴圈

1.

列表for迴圈

for variable in {list}  #有些像C++/CLR中的for each

do

...

done

如：

1.

[[email protected] tmp]# cat b.sh 

#! /bin/bash

for i in 1 2 3 4 5      #1 2 3 4 5等價於{1..5}

do

echo $i

done

[[email protected] tmp]# ./b.sh 

1

2

3

4

5

2.

[[email protected] tmp]# cat b.sh 

#! /bin/bash

for i in $(seq 1 2 6)   #從1增加到6，步幅為2，相當於`seq 1 2 6`

do

echo $i

done

[[email protected] tmp]# ./b.sh 

1

3

5

3.

[[email protected] tmp]# cat b.sh 

#! /bin/bash

for i in $( ls )     #用命令ls的內容替換$( ls )

do

echo $i

done

[[email protected] tmp]# ./b.sh 

1c

a

a1

a1~

...

4.

[[email protected] tmp]# cat b.sh 

#! /bin/bash

for i in "$*"   #把輸入的所有參數看做一個字串整體

do

echo $i

done

[[email protected] tmp]# vim b.sh 

[[email protected] tmp]# ./b.sh 1 2 3

1 2 3

[[email protected] tmp]# cat b.sh 

#! /bin/bash

for i in "[email protected]"  #把輸入的參數分開看待

do

echo $i

done

[[email protected] tmp]# ./b.sh 1 2 3

1

2

3

2.

不帶列表的for迴圈

for variable

do

...

done

相當於

for variable in "[email protected]"

do

...

done

3.

類C風格的for迴圈

for((expr1;expr2;expr3))

do

...

done

如：

for((i=1;i<=100;i+=2))

do

...

done

while迴圈

1.

[[email protected] tmp]# cat b1.sh 

#! /bin/bash

echo "please enter start num:"

read i

echo ""$i"~10:"

while [ "$i" -ne 10 ]

do

echo $i

let "i++"

done

[[email protected] tmp]# ./b1.sh 

please enter start num:

6

6~10:

6

7

8

9

2.類C語言模式

[[email protected] tmp]# cat b1.sh 

#! /bin/bash

echo "please enter start num:"

read i

echo ""$i"~10:"

while ((i!=10))   #注意(())，和[ "$i" -ne 10 ]等價

do

echo $i

let "i++"

done

[[email protected] tmp]# ./b1.sh 

please enter start num:

6

6~10:

6

7

8

9

3.

[[email protected] tmp]# cat b2.sh 

#! /bin/bash

echo "you enter "$#" arguments"  #$#為參數的個數

while [ "$*" != "" ]  #注意空格，等價於[ "$#" != 0 ](把"$#"當做字串)和[ "$#" -ne 0 ]（吧$#當做數字）

do

echo "$1"

shift                        #shift為丟棄第一個參數（$1），然後$1變為$2，$2變為$3以此類推

done

[[email protected] tmp]# ./b2.sh hello world !

you enter 3 arguments

hello

world

!

until迴圈

和while迴圈類似，只是while當條件為真時繼續迴圈，而until當條件為假時繼續迴圈

[[email protected] tmp]# cat b2.sh 

#! /bin/bash

echo "you enter "$#" arguments"

until [ "$#" = 0 ]

do

echo "$1"

shift

done

[[email protected] tmp]# ./b2.sh hello world !

you enter 3 arguments

hello

world

!

控制字元

break 跳出最內層的迴圈

continue 跳出當前迴圈執行下一次的迴圈

select結構

select結構為bash的擴充結構，類似於case，但互動性更好

例：

1.

[[email protected] tmp]# cat b3.sh 

#! /bin/bash

echo "what‘s your favorite color?"

select color in "red" "blue" "green"

do

break

done

echo "you have selected $color"

[[email protected] tmp]# ./b3.sh

what‘s your favorite color?

1) red

2) blue

3) green

#? 2

you have selected blue

2.

[[email protected] tmp]# cat b3.sh 

#! /bin/bash

echo "what‘s your favorite color?"

select color          #相當於select color in "[email protected]"，類似於for color的情況

do

break

done

echo "you have selected $color"

[[email protected] tmp]# ./b3.sh red blue green

what‘s your favorite color?

1) red

2) blue

3) green

#? 2

you have selected blue

本文出自 “flyclc” 部落格，請務必保留此出處http://flyclc.blog.51cto.com/1385758/1540232