Loop syntax in the shell

Loop syntax in the shell

Yun Zhengjie

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A. For Loop1. Syntax format 1

1  for inch Value 1 value 2 value 3 ... 2  Do 3 Source Code 4  Done 　　

2. Syntax Format 2

1  for (initial value; cyclic control condition; variable change)) 2  Do 3 Source Code 4  Done 　　

3. Case show One

1[Email protected] backup]# MoreFor1.SH 2#!/bin/Bash3 # @author: Yinzhengjie4#blog: http://Www.cnblogs.com/yinzhengjie5 #EMAIL: [EMAIL protected]6 7  forIinch 1 2 38      Do9         Echo "The first $i cycle!"Ten  Done One[Email protected] backup]#

4. Case show two (summation)

1[Email protected] backup]# MoreFor3.SH 2#!/bin/Bash3 # @author: Yinzhengjie4#blog: http://Www.cnblogs.com/yinzhengjie5 #EMAIL: [EMAIL protected]6 7 sum=08Read-t --P"Please enter the start number>>>"Startnumber9Read-t --P"Please enter an end number>>>"EndnumberTen  One  for(i= $StartNumber; i<= $EndNumber; i=i+1)) A      Do -         sum=$(($sum+$i)) -  Done the  - Echo "the sum from $startnumber to $endnumber is: $sum" -[Email protected] backup]#

5. Case show three (bulk add users)

1[Email protected] backup]# MoreUseradd.SH 2#!/bin/Bash3 # @author: Yinzhengjie4#blog: http://Www.cnblogs.com/yinzhengjie5 #EMAIL: [EMAIL protected]6 7 8Read-p"Please input username (default"Yinzhengjie"):"-T -username9Read-p"Please input the number of users:"-T -UsersnumberTenRead-p"Please input the password of users:"-T -Password One  A if[ -Z $username] -      Then -Username=Yinzhengjie the fi -  -  - if[!-Z"$username"-A! -Z"$UsersNumber"-A! -Z"$password" ] +      Then -y=$ (Echo$UsersNumber |sed 's/[0-9]//g') +         if[-Z"$y" ] A              Then at                  for((i=1; i<= $UsersNumber; i=i+1 )) -                      Do -Useradd"$username $i"&>/dev/NULL -                         Echo$password |passwd--stdin"$username $i"&>/dev/NULL -                  Done -        fi in fi -  to[Email protected] backup]#

two. While Loopthe while loop is an indefinite loop, also known as a conditional loop. As long as the conditional judgment is established, the cycle will continue. As long as the conditional judgment is not established, the cycle will stop. This is not the same as for the fixed loop. 1. Syntax format

1  while [Conditional judging type] 2  Do 3     Source code 4 done

 2. Case Show

1[Email protected] shell]# More  while.SH 2#!/bin/Bash3 # @author: Yinzhengjie4#blog: http://Www.cnblogs.com/yinzhengjie5 #EMAIL: [EMAIL protected]6 7 sum=08Read-t --P"Please enter the start number>>>"Startnumber9Read-t --P"Please enter an end number>>>"EndnumberTen  One  while[$StartNumber-le $EndNumber] A      Do -         sum=$(( $sum+$StartNumber)) -startnumber=$ (($StartNumber +1 )) the  Done -  -startnumber=$ ($StartNumber-$EndNumber)) -  + Echo "the sum from $startnumber to $endnumber is: $sum" -[Email protected] shell]#

 three. Until CycleThe until loop, in contrast to the while loop, loops as long as the conditional judgment is not true, and executes the loop program. Once the loop condition is established, the loop is terminated. 1. Syntax format

1 until [conditional expression] 2  Do 3     Source code 4 done

2. Case Show

1[Email protected] shell]# More until.SH 2#!/bin/Bash3 # @author: Yinzhengjie4#blog: http://Www.cnblogs.com/yinzhengjie5 #EMAIL: [EMAIL protected]6 7 sum=08Read-t --P"Please enter the start number>>>"Startnumber9Read-t --P"Please enter an end number>>>"EndnumberTen  One until[$StartNumber-GT $EndNumber] A      Do -         sum=$(( $sum+$StartNumber)) -startnumber=$ (($StartNumber +1 )) the  Done -  -startnumber=$ ($StartNumber-$EndNumber)) -  + Echo "the sum from $startnumber to $endnumber is: $sum" -[Email protected] shell]#

Loop syntax in the shell