I have a file that has the following:


First number is the number of times the IP on the right has tried to login into my machine (ssh) from within the same network. Goal is to block that IP using netfilter if the attempt is more than 3. Here, 2 of the entries match the criteria. Note: There might be more than 3 entries.

I can't figure out a way to sort this file line by line (I'm VERY new to BASH). Here is what I tried:

while IFS='' read line || [[ -n "$line" ]]; do
  char1=`awk '{ print $1 }' $file`
  char2=`awk '{ print $2 }' $file`
  if $char1 -gt 3
    echo "$char2 has tried to login $char1 times
done <$file

This gives a "command not found" error pointing to the 5th line (if statement). No wonder, because I echoed $char1_attempt and it gives:

6 13 2
6 13 2
6 13 2

For the time being, J just want it to print out lines like: has tried to login 6 times has tried to login 13 times has tried to login 2 times

Please help!

  • 1
    Replace if $char1 -gt 3 with if [ "$char1" -gt 3 ]. In general, whenever you have a shell syntax error, a good first step is to cut and paste your code into shellcheck.net and correct the errors (important) and warnings (might be important) that it identifies. If you have trouble understanding its messages, then come here and ask. – John1024 Feb 28 '18 at 23:38

I'd recommend starting like this:


while read num addr ; do 
    if [[ "$num" && "$addr" ]] ; then 
        echo "$addr has tried to log in $num times" 
done < "$file"

This way, read stores the first word of each line in $num and the rest of the line in $addr, which should only be the IP address. Then inside the while loop, we check if both are not empty, and if that is the case, print the message.

| improve this answer | |
  • And you can set internal field separator variable for values separated by commas (IFS=","). – Pablo Bianchi Mar 1 '18 at 3:45
  • 1
    What happened to $char1 -gt 3 from the question (Goal is to block that IP using netfilter if the attempt is more than 3.)? Also, adding at least || [[ -n "$num" ]] seems like a good idea to cover the case of the last line not ending in newline. – dessert Mar 1 '18 at 6:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.