find the lines where sequence/sorting is broken in linux

Question

I have a log file which contains lot of logs and first column contains the epoch time stamp, Ideally they should be in sequence/sorted. however if something goes wrong in system timestamp resets to some default value and sequence breaks and restarts. I am trying to find the lines where sequence/sorting is getting borken. Please notice the sequence number in column one.

For example:

101 aaa bbb ccc    
102 aa dd ff gg   
103 asd asd asdas    
104 something goes wrong  
101 restarting the time stamp  
103 new start  
104 going fine   
105 smae here   
102 ahh something unexpected   

Desired output:

104 something goes wrong    
101 restarting the time stamp  

105 smae here   
102 ahh something unexpected 

sort -c helps, but I cannot store its output to any file for further processing. Please let me know if any alternate way is possible.

Answer 1

With awk:

awk '$1 < prev { print saved "\n" $0 "\n" } { prev = $1; saved = $0 }' filename

There's not much to explain here, as you can see:

$1 < prev {                    # if a line is out of order
  print saved "\n" $0 "\n"     # print it and the previous line
}
{                              # and for all lines:
  prev = $1                    # remember the things you need to determine
  saved = $0                   # when that is the case.
}

prev is initially empty and considered equal to zero, which should be fine for Epoch time stamps unless you have log entries from before 1970. If you do, replace $1 < prev with NR > 1 && $1 < prev, since the first line cannot be out of order.