grep dynamically multiple files with customized output

Question

I want to monitor 2 different log files (at the time events appear in logs).

tail -f /var/log/file1 -f /var/log/file2  

For each file, I want to grep some patterns:

tail -f /var/log/file1 | grep '\(pattern1\|pattern2\)'  
tail -f /var/log/file2 | grep '\(pattern3\|pattern4\|pattern5\)' 

I do not know how to have this working all together. Furthermore I would like to print file1 logs output in red and file2 logs output in blue:

Again, I can do it for one file (snippet I grabbed in this forum):

RED='\033[0;31m'
BLUE='\033[0;34m'  

tail -fn0 /var/log/file1 | while read line;
    do
       if echo $line | grep -q '\(pattern1\|pattern2\)';then
          echo -e "{$RED}$line"
       fi
    done

But I absolutely do not know how to do this for multiple files. Any ideas?

Answer 1

If you want to parse multiple logs at the same time, you can use the following syntax:

tail -f /var/log/{log1,log2}

This will produce the desired output of all required logs, so you can then use the -e argument in grep to create multiple patterns. So all together:

tail -f /var/log/{log1,log2} | grep -ie "pattern1" -ie "pattern2" -ie "pattern3"

In regards to colourisation of grep, have a look at this excellent answer.

Answer 2

 tail -n 0 -f file1 file2 |
   awk -v file1pattern="pattern1|pattern2" -v file2pattern="pattern3|pattern4" \
  '/^==> file1 <==$/ { print "\033[0;31m"; pattern=file1pattern };
   /^==> file2 <==$/ { print "\033[0;34m"; pattern=file2pattern }; $0 ~ pattern'

Answer 3

Here is the solution (thank you Mr Kitt and ducks).

How to Tail -f output with colors using only Awk and show the rest of the output?