实战演练
本节将展示一个实用脚本，该脚本在处理用户输入的同时，使用 ping 命令或 ping6 命令来测试与其他网络主机的连通性。
ping 命令或 ping6 命令可以快速测试网络主机是否可用。这个命令很有用，经常作为首选工具。如果只是检查单个主机，那么直接使用该命令即可。
但是如果有数个甚至数百个主机需要检查，则 shell 脚本可以助你一臂之力。

这个脚本通过两种方法来选择要检查的主机：一是使用命令行选项，二是使用文件。下面是
该脚本在 Ubuntu 系统中使用命令行选项的用法演示：

$ ./CheckSystems.sh -t IPv4 192.168.1.102 192.168.1.104 
Checking system at 192.168.1.102... 
[...] 
--- 192.168.1.102 ping statistics --- 
3 packets transmitted, 3 received, 0% packet loss,[...] 
Checking system at 192.168.1.104... 
[...] 
--- 192.168.1.104 ping statistics --- 
3 packets transmitted, 0 received, +3 errors, 100% packet loss,[...] 
$

如果没有指定 IP 地址参数，则脚本会提示用户并退出：

$ ./CheckSystems.sh -t IPv4 
IP Address(es) parameters are missing. 
Exiting script... 
$$ cat CheckSystems.sh 
#!/bin/bash 
# Check systems on local network allowing for 
# a variety of input methods. 
# 
# 
########### Determine Input Method ################### 
# 
# Check for command-line options here using getopts. 
# If none, then go on to File Input Method 
# 
while getopts t: opt 
do case "$opt" in t) # Found the -t option if [ $OPTARG = "IPv4" ] then pingcommand=$(which ping) #elif [ $OPTARG = "IPv6" ] then pingcommand=$(which ping6) # else echo "Usage: -t IPv4 or -t IPv6" echo "Exiting script..." exit fi ;; *) echo "Usage: -t IPv4 or -t IPv6" echo "Exiting script..." exit;; esac # shift $[ $OPTIND - 1 ] # if [ $# -eq 0 ] then echo echo "IP Address(es) parameters are missing." echo echo "Exiting script..." exit fi # for ipaddress in "$@" do echo echo "Checking system at $ipaddress..." echo $pingcommand -q -c 3 $ipaddress echo done exit 
done 
# 
########### File Input Method ################### 
# 
echo 
echo "Please enter the file name with an absolute directory reference..." 
echo 
choice=0 
while [ $choice -eq 0 ] 
do read -t 60 -p "Enter name of file: " filename if [ -z $filename ] then quitanswer="" read -t 10 -n 1 -p "Quit script [Y/n]? " quitanswer #case $quitanswer in Y | y) echo echo "Quitting script..." exit;; N | n) echo echo "Please answer question: " choice=0;; *) echo echo "No response. Quitting script..." exit;; esac else choice=1 fi 
done 
# 
if [ -s $filename ] && [ -r $filename ] 
then echo "$filename is a file, is readable, and is not empty." echo cat $filename | while read line do ipaddress=$line read line iptype=$line if [ $iptype = "IPv4" ] then pingcommand=$(which ping) else pingcommand=$(which ping6) fi echo "Checking system at $ipaddress..." $pingcommand -q -c 3 $ipaddress echo done echo "Finished processing the file. All systems checked." 
else echo echo "$filename is either not a file, is empty, or is" echo "not readable by you. Exiting script..." 
fi 
# 
#################### Exit Script ##################### 
# 
exit 
$