Shellwhile Loop, c-for Loop, until loop, case branch structure, flow control statement

While loop structure

While condition-determining expression

Do

Statement blocks executed when the condition is judged

......

......

Done

Example: Using while to output a number 1 to 10 (ascending output)

J=1

While [$j-le 10]

Do

#useradd wsyht$j

#userdel-R wsyht$i

Echo $j

Let J + + #j =j+1

Done

C-FOR Cycle Structure

for (assigning initial value; condition judgment; step))

Do

Actions performed when the condition is judged

......

Done

For ((i=1;i<=5;i++))

Do

echo "$i"

Sleep 1

Done

<=

<

>=

>

Until cycle structure (the condition judgment is not established to execute the loop body, judging the condition set up cycle termination)

Until conditional-judgment expression

Do

Loop body

.....

Done

Until [1-eq 1]

Do

echo "Wsyht"

Sleep 1

Done

True constancy

FALSE constant false

#!/bin/bash

#while true

#until false

While:

Do

：

#echo "Yht"

#sleep 1

Done

: The position of the conditional expression is constant, and in the body of the loop it means nothing.

Case Branching structure

Execute different commands according to the different values of the variables

Name=yht

Case variable name in

Mode 1)

The action performed when the value of the variable matches the pattern 1;;

......

Mode 2)

The action performed when the value of the variable matches the pattern 2;;

......

Mode 3)

The action performed when the value of the variable matches the pattern 3;;

......

*)

The action performed when the value of the variable does not match any of the above modes;

......

Esac

Cases:

#!/bin/bash

Read-p "Please enter the letter of your choice a | B | C | D "Zimu

Case $zimu in

A

echo "You entered the letter a";;

B

echo "You entered the letter B";;

C

echo "You typed the letter C";;

D

echo "You entered the letter D";;

*）

echo "$ only Select a | B | C | D in one of the "

Esac

Case is usually used with a function to write a startup script to the service

Process Control Statements

Break continue operation pair like a looping structure

Break

Jump out of the current loop body

Continue

End this cycle and start the next cycle

Exit

Exit script default return value is 0

Return

return value only, no exit, use in function, set return value of function

Shift (position move function)

Used to migrate location variables, pass $1-$N values to the left, and delete variables with no value

Example 1:

$ $

Ten shift

Shift

Shift

Example 2: Example 3:

#!/bin/bashi=0

Echo $#while [$#-GT 0]

echo $ do

Shifti= ' expr $i + $ '

echo $#shift

echo $ $ done

ShiftEcho $i

Echo $#

Echo $ $

Cases:

#!/bin/bash

For ((i=1;i<=9;i++))

Do

If [$i-eq 9]

#break

#continue

#exit 2

Fi

Echo $i

Done

This article is from the "Wsyht blog" blog, make sure to keep this source http://wsyht2015.blog.51cto.com/9014030/1786326

Shellwhile Loop, c-for Loop, until loop, case branch structure, flow control statement