如何检查文件中存在的子字符串？

Question

I want to write some rules in a file with a shell script . But Before adding any rule i want to check some conditions . This is my file:

Example :

i wrote some rule like :

/home/Desktop/myfile.txt

iptables -t nat -A PREROUTING -p tcp -m tcp --dport 666 -j DNAT --to-destination 192.168.19.55
iptables -t nat -A PREROUTING -p tcp -m tcp --dport 633 -j DNAT --to-destination 192.168.19.44
iptables -t nat -A PREROUTING -p tcp -m tcp --dport 656 -j DNAT --to-destination 192.168.19.88

Now if the file contains same port and IP at the time of adding new rule , the script should print rule exist already . If only port present in the existing file , script should print port already in use . Otherwise , i want to print success .

that is

case 1 : if i add 666 port with 192.168.19.55 IP , the script should print rule already exist .
case 2 :  if i add 666 port with 192.168.66.55 IP , the script should print port already used  .
case 3 : otherwise script print success . 

I tried to write simple shell script with arguments as IP and port:

#!/bin/shell
if [ $# -eq 2 ] 
then
    //How to check the above conditions with file /home/Desktop/myfile.txt ??
    //Need to add this rule to the myfile.txt 
    iptables -t nat -A PREROUTING -p tcp -m tcp --dport $2 -j DNAT --to-destination $1
else
    echo "invalid arguments"
fi

Answer 1

You can use grep to check the contents of the file. Note that . is special in regular expressions, so I used parameter expansion to replace it with \\. that matches the dot literally.

#!/bin/bash

config=/home/Desktop/myfile.txt

ip=$1
port=$2

if grep -q -- "--dport $port .*--to-destination ${ip//./\\.}$" "$config"; then
    echo Rule already exists. >&2
    exit 1

elif grep -q -- "--dport $port " "$config"; then
    echo Port already used. >&2
    exit 1

else
    echo iptables -t nat -A PREROUTING -p tcp -m tcp --dport $port -j DNAT --to-destination $ip
fi

This is just an example. In reality, port and destination might appear in different order in the config file, so the expressions would be more complex. It might be easier to generate the file from a file that only contains the required information in a given format (ie two columns, destination and port).

Answer 2

awk -v port=$1 -v ip=$2 '($11 == port && $15 == ip) { print "rule already exists"  } ($11 == port && $15 != ip) { print "Port already in use" } ($11 != port && $15 != ip) { print "success";system("iptables -t nat -A PREROUTING -p tcp -m tcp --dport "$2" -j DNAT --to-destination "$1) }' myfile.txt

使用awk，我们可以集中第11个以空格分隔的端口数据和第15个以ip地址存储的数据，并根据所传递的用于端口和IP的参数进行检查，并根据特定条件打印所需的文本，然后在iptables命令上运行成功。