Pattern matching for log analysis

My program will issue a grep command to search the log base on time range and a unique key word. My program able to issued out the grep command successfully and it’s return several matched line of log which look like the following:

22:41.9 INFO    SSHD    SSHD-TRANSFER-1 [accountName=root] [remoteAddress=/172.16.8.1:64931]:Logout agent success [accountName=null remoteAddress=STEDGE/172.16.8.3]    AuthenticationProviderImpl.java com.tumbleweed.st.server.sshd.AuthenticationProviderImpl    executeLogoutAgent  429 UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN
21:45.9 INFO    SSHD    SSHD-TRANSFER-1 [accountName=root] [remoteAddress=/172.16.8.1:64931]:Invoking logout agent [accountName=null remoteAddress=STEDGE/172.16.8.3]   AuthenticationProviderImpl.java com.tumbleweed.st.server.sshd.AuthenticationProviderImpl    executeLogoutAgent  425 UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN
21:45.9 INFO    SSHD    SSHD-TRANSFER-1 [accountName=root] [remoteAddress=/172.16.8.1:64931]:SSH: User "null" logged out from [172.16.8.1]. AuthenticationProviderImpl.java com.tumbleweed.st.server.sshd.AuthenticationProviderImpl    executeLogoutAgent  422 UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN

But I don’t need all of this, the things I am interested in is [remoteAddress=/172.16.8.1:64931]. This line of code Pattern pat1 = Pattern.compile("remoteAddress=/(d)"); giving the illegal escape character. May I know how to extract out the IP address only without any port number and store it into a String variable, I had searched some information on google but it fails to work.

For your reference, this is my source code:

import java.io.*;
import java.util.regex.*;
class blockIP
{
   public static void main(String [] args)
   {
     String command1 = "date +%R";
     String time = null;
     String argument2 = null;
     String argument1 = ".*java";
     try
       {
             Process p1 = Runtime.getRuntime().exec(command1);
             BufferedReader br1 = new BufferedReader(new InputStreamReader(p1.getInputStream()));
             
             String line1;
             while((line1 = br1.readLine()) != null )
              {
                  System.out.println(line1);
                  time = line1;
                  argument2 =time.concat(argument1);
              }
           br1.close();
           String command2 = "grep "+argument2+" stlog.txt";
           System.out.println("the command2 is :"+command2);
           Process p2 = Runtime.getRuntime().exec(command2);
           BufferedReader br2 = new BufferedReader(new InputStreamReader(p2.getInputStream()));
           String line2;
           while((line2 = br2.readLine()) != null)
           { 
              System.out.println(line2);
              Pattern pat1 = Pattern.compile("remoteAddress=/(d)");
              Matcher matcher1 = pat1.matcher(line2);
              while(matcher1.find())
                   {
                     System.out.println(matcher1.group(1));
                   }
           }
      }
      catch(IOException e)
      {
        e.printStackTrace();
      }
    
   }
}

Answer

This regex matches digits and dots after remoteAddress=/ phrase.

public static void main(String[] args) {
        String s = "21:45.9 INFO    SSHD    SSHD-TRANSFER-1 [accountName=root] [remoteAddress=/172.16.8.1:64931]:Invoking logout agent [accountName=null remoteAddress=STEDGE/172.16.8.3]   AuthenticationProviderImpl.java com.tumbleweed.st.server.sshd.AuthenticationProviderImpl    executeLogoutAgent  425 UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWN UNKNOWNrn";
        Pattern pattern = Pattern.compile("(?<=remoteAddress=/)[\d.]+");
        Matcher matcher = pattern.matcher(s);
        while (matcher.find()) {
            String group = matcher.group();
            System.out.println(group);
        }

    }

It won’t match remoteAddress=STEDGE/172.16.8.3.

It uses positive lookbehind to assert that (?<=remoteAddress=/) is before 172.16.8.1

Pattern:

(?<=remoteAddress=/) positive lookbehind(zero-length assertion). It matches only if [\d.]+ is preceded by exact phrase remoteAddress=/.

[\d.]+ match digit or period . for 1 or more times. Doesn’t match anything else.