for循環

1.

列表for循環

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

do

...

done

如：

1.

[root@localhost tmp]# cat b.sh?

#! /bin/bash

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

do

echo $i

done

[root@localhost tmp]# ./b.sh?

1

2

3

4

5

2.

[root@localhost tmp]# cat b.sh?

#! /bin/bash

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

do

echo $i

done

[root@localhost tmp]# ./b.sh?

1

3

5

3.

[root@localhost tmp]# cat b.sh?

#! /bin/bash

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

do

echo $i

done

[root@localhost tmp]# ./b.sh?

1c

a

a1

a1~

...

4.

[root@localhost tmp]# cat b.sh?

#! /bin/bash

for i in "$*" ? #把輸入的所有參數看做一個字符串整體

do

echo $i

done

[root@localhost tmp]# vim b.sh?

[root@localhost tmp]# ./b.sh 1 2 3

1 2 3

[root@localhost tmp]# cat b.sh?

#! /bin/bash

for i in "$@" ?#把輸入的參數分開看待

do

echo $i

done

[root@localhost tmp]# ./b.sh 1 2 3

1

2

3

2.

不帶列表的for循環

for variable

do

...

done

相當于

for variable in "$@"

do

...

done

3.

類C風格的for循環

for((expr1;expr2;expr3))

do

...

done

如：

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

do

...

done

while循環

1.

[root@localhost 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

[root@localhost tmp]# ./b1.sh?

please enter start num:

6

6~10:

6

7

8

9

2.類C語言模式

[root@localhost 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

[root@localhost tmp]# ./b1.sh?

please enter start num:

6

6~10:

6

7

8

9

3.

[root@localhost tmp]# cat b2.sh?

#! /bin/bash

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

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

do

echo "$1"

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

done

[root@localhost tmp]# ./b2.sh hello world !

you enter 3 arguments

hello

world

!

until循環

和while循環類似，只是while當條件為真時繼續循環，而until當條件為假時繼續循環

[root@localhost tmp]# cat b2.sh?

#! /bin/bash

echo "you enter "$#" arguments"

until [ "$#" = 0 ]

do

echo "$1"

shift

done

[root@localhost tmp]# ./b2.sh hello world !

you enter 3 arguments

hello

world

!

控制字符

break 跳出最內層的循環

continue 跳出當前循環執行下一次的循環

select結構

select結構為bash的擴展結構，類似于case，但交互性更好

例：

1.

[root@localhost 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"

[root@localhost tmp]# ./b3.sh

what's your favorite color?

1) red

2) blue

3) green

#? 2

you have selected blue

2.

[root@localhost tmp]# cat b3.sh?

#! /bin/bash

echo "what's your favorite color?"

select color ? ? ? ? ?#相當于select color in "$@"，類似于for color的情況

do

break

done

echo "you have selected $color"

[root@localhost tmp]# ./b3.sh red blue green

what's your favorite color?

1) red

2) blue

3) green

#? 2

you have selected blue

轉載于:https://blog.51cto.com/flyclc/1540232

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