When you type long commands like this one to display only certain fields of the squid log file.

tail -f  /var/log/squid/access.log | awk '{print $3,$4,$5,$7,$9}'

You do not want to type it again, every time you need it, so, you use history, you can find it by using.

history | grep tail

You will see an output like this

 967  tail -f  /var/log/squid/access.log | awk '{print $3,$4,$5,$7,$9}'

And then run it with:

!967

or you can run

!tail

And history will search for the command starting with tail, and will execute it.