You don't seem to understand the concept of a pipeline. In a pipeline, the standard output from the first command in the pipeline becomes the standard input to the second command in the pipeline. If there are more than two commands in the pipeline, the output from every command in the pipeline but the last become the standards input for the next command in the pipeline. And all stages in the pipeline are free to run asynchronously as long as each command reading from its standard input has data to read and each process writing data to the next element of the pipeline is still there to read from the pipe. But in your pipeline:

Code:

tail -f /var/log/apache2/access.log |
  awk '/debug/{print $1 >> "ip2"}' |
  awk '!a[$0]++' ip2 >> ip |
  echo "$prefix$ip" > fail2ban_ip |
  sed -e 's/$/ -p tcp -dports 80 -j DROP/' -i fail2ban_ip > block |
  chmod 755 block |
  ./block

The first awk command writes nothing to standard output. The second awk does not read anything from its standard input. (It reads from a file named ip2 which might or might not exist when that awk tries to open it since it is being created asynchronously by the previous awk. If the file does exist, there is a good chance that it will be processed by the 2nd awk before the 1st awk adds anything to it.) And, the second awk creates a file named ip, but does not write anything to the next stage of the pipeline, but that may be OK because echo never reads from its standard input. Note also that the variable ip which is being passed to echo is not defined by this script. And, since the output from echo is directed to a file, again nothing is written to the standard input of the next stage of the pipeline. But, again, that may be OK because sed when given a filename operand does not read from its standard input. And, sed when invoked with a -i option either gives you a syntax error for an unrecognized option or updates its input file in place. In either of these cases sed writes nothing to its standard output, so the file created by the redirection of standard output from sed will be an empty file. Then we have the next stage of the pipeline (chmod 755 block) which neither reads from standard input nor writes to standard output. And, finally, we have the last stage of the pipeline (./block) which either executes an empty file (if the chmod completed before this stage starts) or fails because it is not executable (if the file hadn't been created yet, or had been created but had not yet been made executable).

I don't know what you are trying to do with this pipeline, but there are so many different concurrent operations going on here with nothing to guarantee that they happen in the proper sequence that the actual behavior will vary considerably depending on what shell you use to run this script, what operating system you use to run this script, the number of other processes that are running on the system when you run this script, and the phase of the moon.

I don't have an apache2 access log file to look at, so I have no idea what is in some of the data you seem to be trying to extract from records in that file. And, you haven't really given us an explanation of what you are trying to do with this script. Without a much better description of what you're trying to do and a sample log file to use as a test case, I don't see how I can help you.