Shulou(Shulou.com)06/02 Report--

In this issue, the editor will bring you how to understand the linux for cycle. The article is rich in content and analyzes and narrates it from a professional point of view. I hope you can get something after reading this article.

The for loop is the most commonly used structure in Linux shell. For loops have three structures: one is a list for loop; the second is a for loop without a list; and the third is a C-like for loop.

For var in list

Do

Commands

Done

#! / bin/bash

For test in alabama alaska arizona arkansas california colorado

Do

Echo the next state is $test

Done

>

The next state is alabama

The next state is alaska

The next state is arizona

The next state is arkansas

The next state is california

The next state is colorado

#! / bin/bash

For test in alabama alaska arizona arkansas california colorado

Do

Echo "the next state is $test"

Done

Echo "The las state we visited was $test"

Test=connecticut

Echo "wait, now we're visiting $test"

>

The next state is alabama

The next state is alaska

The next state is arizona

The next state is arkansas

The next state is california

The next state is colorado

The las state we visited was colorado

Wait, now we're visiting connecticut

#! / bin/bash

For test in I don't know if this'll work

Do

Echo "word:$test"

Done

>

Word:I

Word:dont know if thisll

Word:work

#! / bin/bash

For test in nevada "New Hampshire"New Mexico"New York"

Do

Echo "Now going to $test"

Done

>

Now going to nevada

Now going to New Hampshire

Now going to New Mexico

Now going to New York

#! / bin/bash

List= "Alabama ALaska Arizona Arkansas Colorado"

List=$list "Connecticut"

For state in $list

Do

Echo "Have you ever visited $state?"

Done

>

Have you ever visited Alabama?

Have you ever visited ALaska?

Have you ever visited Arizona?

Have you ever visited Arkansas?

Have you ever visited Colorado?

Have you ever visited Connecticut?

#! / bin/bash

File= "states"

For state in `cat $file`

Do

Echo "Visit beautiful $state"

Done

# cat states

>

Alabama

Alaska

Dddfac

Dfsase

Cvcvss

Dfqzcvc

Ddddwq

Bnnn

Qqojfaso

>

Visit beautiful Alabama

Visit beautiful Alaska

Visit beautiful dddfac

Visit beautiful dfsase

Visit beautiful cvcvss

Visit beautiful dfqzcvc

Visit beautiful ddddwq

Visit beautiful bnnn

Visit beautiful qqojfaso

#! / bin/bash

IFS=$'\ n'

File= "states"

For state in `cat $file`

Do

Echo "visit beautiful $state"

Done

>

# cat states

>

A labama

Alaska

Dddfac

Dfsase

Cvcvss

Dfqzcvc

Ddddwq

Bnnn

Qqojfaso

>

Visit beautiful A labama

Visit beautiful Alaska

Visit beautiful dddfac

Visit beautiful dfsase

Visit beautiful cvcvss

Visit beautiful dfqzcvc

Visit beautiful ddddwq

Visit beautiful bnnn

Visit beautiful qqojfaso

When dealing with long scripts, you may need to change the value of IFS in one place, then forget about it and think it is the default value elsewhere in the script. A simple practice to refer to:

IFS.OLD=$IFS

IFS=$'\ n'

IFS=$IFS.OLD

#! / bin/bash

For file in / root/*

Do

If [- d "$file"] then

Echo "$file is a directory"

Elif [- f "$file"] then

Echo "$file is a file"

Fi

Done

#! / bin/bash

For file in / root/.b* / home/rich/badtest

Do

If [- d "$file"] then

Echo "$file is a directory"

Elif [- f "$file"] then

Echo "$file is a file"

Else

Echo "$file doesn't exist"

Fi

Done

C-like language style

#! / bin/bash

For ((iTun1; ido)

Echo "The next nuber is $I"

Done

>

The next nuber is 1

The next nuber is 2

The next nuber is 3

The next nuber is 4

The next nuber is 5

The next nuber is 6

The next nuber is 7

The next nuber is 8

The next nuber is 9

The next nuber is 10

#! / bin/bash

For ((axi1, baux10; a do)

Echo "$a-$b"

Done

>

1-10

2-9

3-8

4-7

5-6

6-5

7-4

8-3

9-2

10-1

11-0

12-1 above is how the linux for cycle shared by the editor is understood. If you happen to have similar doubts, you might as well refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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