/ 2018-09-27
已知:/etc/hosts的内容为
192.168.1.11 oldboy11.oldboyedu.com
192.168.1.21 oldboy21.oldboyedu.com
192.168.1.31 oldboy31.oldboyedu.com
#192.168.1.111 oldboy111.oldboyedu.com
请用shell脚本实现,怎么才能在输入IP后找到/etc/hosts里对应的唯一的hostname?
解答:
法一、脚本过滤法
[root@old_boy scripts]# cat judgehost.sh #!/bin/bash echo "please input ip address:" read ip [ -n "`grep "$ip " /etc/hosts`" ] && \ #注意前面的过滤条件结尾带有空格。 echo "The hostname is: `grep "$ip " /etc/hosts |awk '{print $2}'`" || \ echo "The ip is invalid"
提示:
1)这是一个grep过滤加条件判断的实现语法:
2)条件判断语法为[ -n "ddd" ] && echo 1 || echo 0
3)[ -n "`grep "$ip " /etc/hosts`" ] && \ #注意前面的过滤条件结尾带有空格。这里啊,是为了排除下面的重复情况
192.168.1.11 oldboy11.oldboyedu.com
192.168.1.111 oldboy111.oldboyedu.com
法二、脚本精确匹配法:
#!/bin/bash #author oldboy #qq 31333741 #judge input if [ $# -ne 1 ] then echo "input error!" exit 1 fi flag=0 exec < /etc/hosts while read line do if [ "$1" = "`echo $line|awk '{print $1}'`" ] then flag=1 echo "the $1 's hostname is `echo $line|awk '{print $2}'`" break; fi done [ $flag -eq 0 ] && echo " sorrry,not find $1 's hostname!" 提示:此题,请大家学习while的用法及设置flag的思路。 执行结果: [root@old_boy scripts]# sh oldboy.sh 192.168.1.11 the 192.168.1.11 's hostname is oldboy11.oldboyedu.com [root@old_boy scripts]# sh oldboy.sh 192.168.1.21 the 192.168.1.21 's hostname is oldboy21.oldboyedu.com [root@old_boy scripts]# sh oldboy.sh 192.168.1.311 sorrry,not find 192.168.1.311 's hostname!
特别提示:下面的方法中,老男孩老师大量的使用了awk的不同方法来实现同样的功能,来告诉大家,awk是很强大的, 希望同学们能按照老师的教学要求精通之。
法三、awk精确匹配:
准备:
[root@old_boy scripts]# tail -4 /etc/hosts 192.168.1.11 oldboy11.oldboyedu.com 192.168.1.111 oldboy111.oldboyedu.com 192.168.1.21 oldboy21.oldboyedu.com 192.168.1.31 oldboy31.oldboyedu.com
脚本:
[root@old_boy scripts]# cat awkhost1.sh awk 'BEGIN {a="'$1'"} {if($1==a) print $2; }' /etc/hosts 执行结果: [root@old_boy scripts]# sh awkhost1.sh 192.168.1.21 oldboy21.oldboyedu.com [root@old_boy scripts]# sh awkhost1.sh 192.168.1.31 oldboy31.oldboyedu.com [root@old_boy scripts]# sh awkhost1.sh 192.168.1.11 oldboy11.oldboyedu.com
提示:注意a="'$1'"的用法,$1为命令行传参。awk程序中调用系统变量的方法a="'$1'"。
法四、awk精确匹配法
[root@old_boy scripts]# cat awkhost2.sh awk '{if($1=="'$1'") print $2}' /etc/hosts 执行结果: [root@old_boy scripts]# awkhost2.sh 192.168.1.11 oldboy11.oldboyedu.com [root@old_boy scripts]# awkhost2.sh 192.168.1.21 oldboy21.oldboyedu.com [root@old_boy scripts]# awkhost2.sh 192.168.1.311
法五、awk过滤法
[root@old_boy scripts]# cat awkhost4.sh awk '/'"${1} "'/''{print $2}' /etc/hosts 执行结果: [root@old_boy scripts]# awkhost4.sh 192.168.1.21 oldboy21.oldboyedu.com [root@old_boy scripts]# awkhost4.sh 192.168.1.11 oldboy11.oldboyedu.com [root@old_boy scripts]# awkhost4.sh 192.168.1.31 oldboy31.oldboyedu.com 提示:除了语法外,这道题有个学问,就是过滤时传参结尾要带个空格,这样才能过滤重复IP的情况 如: 192.168.1.11 oldboy11.oldboyedu.com 192.168.1.111 oldboy111.oldboyedu.com
法六、awk过滤法
[root@old_boy scripts]# cat awkhost5.sh awk '{if($1~/'$1'/) print $2}' /etc/hosts ##如果文件第一列包含命令行第一个参数字符则打印第二列 执行结果: [root@old_boy scripts]# awkhost5.sh 192.168.1.31 oldboy31.oldboyedu.com [root@old_boy scripts]# awkhost5.sh 192.168.1.11 oldboy11.oldboyedu.com oldboy111.oldboyedu.com ------>这里有bug了。 [root@old_boy scripts]# awkhost5.sh 192.168.1.21 oldboy21.oldboyedu.com 改进下来排除bug: [root@old_boy scripts]# cat awkhost5-1.sh awk '{if($1~/'$1' /) print $2}' /etc/hosts ==>用上面加空格的思路不对。 [root@old_boy scripts]# cat awkhost5-1.sh awk '{if($1~/'$1'$/) print $2}' /etc/hosts #增加一个正则表达式$ 执行结果: [root@old_boy scripts]# awkhost5-1.sh 192.168.1.21 oldboy21.oldboyedu.com [root@old_boy scripts]# awkhost5-1.sh 192.168.1.11 oldboy11.oldboyedu.com [root@old_boy scripts]# awkhost5-1.sh 192.168.1.31 oldboy31.oldboyedu.com
法七、awk -v精确匹配法
命令行测试: [root@old_boy scripts]# awk -v p=192.168.1.21 '$1 == p{print $2}' /etc/hosts oldboy21.oldboyedu.com [root@old_boy scripts]# awk -v p=192.168.1.11 '$1 == p{print $2}' /etc/hosts oldboy11.oldboyedu.com [root@old_boy scripts]# awk -v p=192.168.1.11 '$1 == p {print $2}' /etc/hosts oldboy11.oldboyedu.com 实际脚本: [root@old_boy scripts]# cat awkhost6.sh #!/bin/bash #p=$1 #awk -v p="$p" '$1 == p{print $2}' /etc/hosts awk -v p="$1" '$1 == p{print $2}' /etc/hosts 执行结果: [root@old_boy scripts]# sh awkhost6.sh 192.168.1.11 oldboy11.oldboyedu.com [root@old_boy scripts]# sh awkhost6.sh 192.168.1.21 oldboy21.oldboyedu.com
提示:
1)传参非awk程序,因此写法p="$1"
2)man awk
-v var=val
--assign var=val
Assign the value val to the variable var, before execution of the program begins. Such variable values are available to the BEGIN block of an AWK program.
法八、精确匹配简单的写法
[root@old_boy scripts]# cat awkhost9.sh awk '$1 == "'$1'" {print $2}' /etc/hosts 执行结果: [root@old_boy scripts]# sh awkhost9.sh 192.168.1.11 oldboy11.oldboyedu.com [root@old_boy scripts]# sh awkhost9.sh 192.168.1.21 oldboy21.oldboyedu.com [root@old_boy scripts]# sh awkhost9.sh 192.168.1.31 oldboy31.oldboyedu.com
法九、一个不成熟的实现法
#!/bin/bash #author oldboy #qq 31333741 hosts_file="$PWD/oldboy.txt" #judge file [ ! -f $hosts_file ] && echo "no test file!" && exit 1 echo -n "plase input ip : " read ip #judge ip format [ "${#a}" -lt 8 ] && [ "`echo $ip|sed 's/[0-9]//g'`" != "..." ] && \ echo "Plase input the correct IP address" && exit 1 #start result1=$(grep "$ip" $hosts_file|awk '{print $1}') if [ "$ip" == "$result1" ] then grep "$ip" $hosts_file|awk '{print $2}' exit 0 else echo "Not find the hostname of $ip" exit 1 fi 提示:此法不可取,画蛇添足了。
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