For loop of shell script

shell The script for loop

Circulatory ：for、while、until

What is? for Circulation? ？

for Circular logic : It is to assign the elements in the circular list to variables , Each assignment will execute a loop ,done It marks the end of a cycle . Until the elements in the list are exhausted , End the cycle （ You can understand that , Because of something , You make your partner angry , Do you have to apologize , It's no use apologizing once , Is it a second time , It's a cycle Until your partner forgives you This cycle ends . You can understand that ）

Format ：

for Variable in value 1 value 2 value 3

do It is equivalent to the upper part of the brace

echo Statement program

done Equivalent to the lower part of the brace

Bring each value into your variable and enter one by one Then output the waiting set

!

Application example ：1

The first format $* Treat all parameters as a whole

Second format [email protected] Indicates that each parameter is partitioned

stay It can be seen when the quantity is large $\ast and$@ What's the difference

Case study ：

$* The output is a whole

vim textfor.sh

Comment on the environment #！/bin/bash

for i in "$\ast \ast "thisindividualyesWhatWellIt\; meansthinking:yeshold$* * Assign to i This variable hold &* Give this value to i Then output him echo Things that are If it's one time Just output once If it's separate That's it Multiple corresponding outputs

do

echo “the num is $i”

done

chmod 744 perhaps +x textfor.sh Give an executive authority

./textfor.sh perform

[email protected] Separate output

vim textfor.sh

Comment on the environment #！/bin/bash

for i in “[email protected]”

do

echo"the num is $i"

done

chmod 744 perhaps +x textfor.sh Give an executive authority

./textfor.sh 10 20 30 perform

Handled separately Pay attention to $\ast and$@ What's the difference

$* Overall treatment

[email protected] Separate the

Like hold 10 20 30 I don't know the number of the sum of the values of To use [email protected] It's convenient

The second basic grammar

for（ Initial value ; Cycle control conditions ; Variable change ）

do

Program

done

Case study from 1 Add to 100 The value output of 1 All the way up to 100

vim testfor2.sh Create a for Script for

!/bin/bash

sum=0 When sum It means and

for((i=1;i<=100;i++)) What does it mean in parentheses i be equal to 1 ;i<=100 It means when i Greater than or equal to 100 when ;i++ It means i++ It's using i Then add another
do
SUM=$[$SUM+$i] In parentheses is a cumulative In brackets sum and i After accumulation, give it to the front sum Then output the final result Note that brackets are used here 【】

done
echo “SUM=$SUM” Output the final result

~

chmod 744 perhaps +x textfor.sh Give an executive authority

./testfor2.sh

2.3 Multiplication table
utilize for loop , Print 99 Multiplication table
#!/bin/bash
for ((i=1;i<=9;i++)) # You can also write here for i in {1…9}
do
for ((j=1;j<=i;j++)) # You can also write here for j in seq $i
do echo -n -e “$j\ast$i=$[j*i]\t” #-n Don't wrap output ;-e Use \ Escape character ;\t Horizontal tabulation ; If not -e, be \t Is a normal character
done
echo
done

3、 ... and . summary
1.for Loops are widely used in actual generation , Avoid manual repetition to operate something
2.for The list in the loop supports regular expressions
3.for Use in loop (()), Support in double brackets C The command of language
4.for Variables in the loop , Just cycle to get values from the list , Then proceed do operation , So the number of parameters in the value list , Determines the number of cycles