When you work with a squid access log file you sometimes want to know when a site or resource was accessed. Squid does not store the date and time information for that in a human readable format.
It is stored as <unix timestamp>.<centisecond> so you can use a command like that to post-process to make it more readable for you:
cat access.log | perl -p -e 's/^([0-9]*)/"[".localtime($1)."]"/e'