shell多种方法解决一道实用linux运维问题!
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4)已知:/etc/hosts的内容为
192.168.1.11oldboy11.etiantian.org
192.168.1.21oldboy21.etiantian.org
192.168.1.31oldboy31.etiantian.org
#192.168.1.111oldboy111.etiantian.org
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1)脚本过滤法
[*] # 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
192.168.1.11oldboy11.etiantian.org
192.168.1.111oldboy111.etiantian.org
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法2)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: # sh oldboy.sh 192.168.1.11
the 192.168.1.11 's hostname is oldboy11.etiantian.org
# sh oldboy.sh 192.168.1.21
the 192.168.1.21 's hostname is oldboy21.etiantian.org
# sh oldboy.sh 192.168.1.311
sorrry,not find 192.168.1.311 's hostname!
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特别提示:下面的方法中使用了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
法3)awk精确匹配:
准备:
# tail -4 /etc/hosts
192.168.1.11oldboy11.etiantian.org
192.168.1.111oldboy111.etiantian.org
192.168.1.21oldboy21.etiantian.org
192.168.1.31oldboy31.etiantian.org
脚本:
[*] # cat awkhost1.sh
[*] awk 'BEGIN {a="'$1'"} {if($1==a) print $2; }' /etc/hosts
执行结果:
# sh awkhost1.sh 192.168.1.21
oldboy21.etiantian.org
# sh awkhost1.sh 192.168.1.31
oldboy31.etiantian.org
# sh awkhost1.sh 192.168.1.11
oldboy11.etiantian.org
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'"。
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法4)awk精确匹配法
[*] # cat awkhost2.sh
[*] awk '{if($1=="'$1'") print $2}' /etc/hosts
执行结果:
# awkhost2.sh 192.168.1.11
oldboy11.etiantian.org
# awkhost2.sh 192.168.1.21
oldboy21.etiantian.org
# awkhost2.sh 192.168.1.311
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法5)awk过滤法
[*] # cat awkhost4.sh
[*] awk '/'"${1} "'/''{print $2}' /etc/hosts
[*] 执行结果:
[*] # awkhost4.sh 192.168.1.21
[*] oldboy21.etiantian.org
[*] # awkhost4.sh 192.168.1.11
[*] oldboy11.etiantian.org
[*] # awkhost4.sh 192.168.1.31
[*] oldboy31.etiantian.org
[*] 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:
[*] 192.168.1.11oldboy11.etiantian.org
[*] 192.168.1.111oldboy111.etiantian.org
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法6)awk过滤法
[*] # 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:
[*] # awkhost5.sh 192.168.1.31
[*] oldboy31.etiantian.org
[*] # awkhost5.sh 192.168.1.11
[*] oldboy11.etiantian.org
[*] oldboy111.etiantian.org ------>这里有bug了。
[*] # awkhost5.sh 192.168.1.21
[*] oldboy21.etiantian.org
[*] 改进下来排除bug:
[*] # cat awkhost5-1.sh
[*] awk '{if($1~/'$1' /) print $2}'/etc/hosts ==>用上面加空格的思路不对。
[*] # 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:
[*] # awkhost5-1.sh 192.168.1.21
[*] oldboy21.etiantian.org
[*] # awkhost5-1.sh 192.168.1.11
[*] oldboy11.etiantian.org
[*] # awkhost5-1.sh 192.168.1.31
[*] oldboy31.etiantian.org
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法7)awk -v精确匹配法
[*] 命令行测试:
[*] # awk -v p=192.168.1.21 '$1 == p{print $2}' /etc/hosts
[*] oldboy21.etiantian.org
[*] # awk -v p=192.168.1.11 '$1 == p{print $2}' /etc/hosts
[*] oldboy11.etiantian.org
[*] # awk -v p=192.168.1.11 '$1 == p {print $2}' /etc/hosts
[*] oldboy11.etiantian.org
[*] 实际脚本:
[*] # 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:
# shawkhost6.sh192.168.1.11
oldboy11.etiantian.org
# shawkhost6.sh192.168.1.21
oldboy21.etiantian.org
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. Suchvari-
able values are available to the BEGIN block of an AWK program.
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法8:精确匹配简单的写法
[*] # cat awkhost9.sh
[*] awk'$1 == "'$1'" {print $2}' /etc/hosts
[*] 执行结果:
[*] # sh awkhost9.sh192.168.1.11
[*] oldboy11.etiantian.org
[*] # sh awkhost9.sh192.168.1.21
[*] oldbo.org
[*] # sh awkhost9.sh192.168.1.31
[*] oldboy31.etiantian.org
[*] 特别提示:这里大量的使用了awk的不同方法来实现同样的功能,很强大吧。
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法9:一个不成熟的实现法
[*] #!/bin/bash
[*] b=/$PWD/wang.txt
[*] echo -n "plase input ip : "
[*] read a
[*] if [ $a == "192.168.1.11" ]
[*] then
[*] cat $b | grep $a | awk -F ' ''{print $2}'
[*]
[*] elif [ $a== "192.168.1.21" ]
[*] then
[*] cat $b | grep $a | awk -F ' ''{print $2}'
[*]
[*] elif [ $a== "192.168.1.31" ]
[*] then
[*] cat $b | grep $a | awk -F ' ''{print $2}'
[*] else
[*] echo "plase input the correct IP address " && exit 1
[*] fi
[*] 提示:大家看看问题在哪?脚本不通用。
[*]
----------改进后
[*] #!/bin/bash
[*] #author oldboy
[*] #qq 541376442
[*] hosts_file="$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 $ip|sed 's///g'`" != "..." ] && \
[*] echo "Plase input the correct IP address" && exit 1
[*]
[*] #start
[*] result1=$(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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