Shell script-traverse the IP address in a for loop

• Requirement: Check whether the IP address is online
  In order to prevent the online server from conflicting with the IP address of the online network, write a shell script to list and save the online IP addresses and offline IP addresses of the 20.0.0.0/24 network segment To the document.

• Analysis:
  1. There are 254 public IP addresses in the 24 network segment, from 20.0.0.1 to 20.0.0.254, which need to be traversed in a for loop.
  2. To see if an IP address is online, use the ping command to test

• step:

  #!/bin/bash
  b="20.0.0."          ###将网段赋值于b
  for a in `seq 1 254`        ### 将 1-254个地址赋值于a，做for循环遍历
  do
  ping -c 2 $b$a > /dev/null        ###ping这个网段的所有地址，将其信息导入/dev/null文件中（ping中所带的-c 2 是2个包的意思，还有-i 、 -w； 示例：ping -c 2 -i 0.5 -w 3 意思为ping 2个包、间隔0.5秒、时延3秒）
  if [ $? -eq 0 ];then            ####判定ping其中的网址参数是否为0
  echo "$b$a is online" >> ip遍历1.txt       ###为0 则输出这个网址是online状态的并追加到ip遍历.txt 这个文件中
  else      ###否则
  echo "$b$a is not online" >> ip遍历2.txt    ###则输出这个网址是not online状态的并追加到ip遍历.txt 这个文件中
  fi
  done
  

• Verification:
  View the information in the file ip traversal 1.txt and file ip traversal 2.txt. The data in
  ip traversal 1.txt are all online
  . The data in ip traversal 2.txt are all not online.

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That's it, thanks for watching