How to convert Unix time to human readable format

Unix-like operating systems maintain time as the number of seconds elapsed since midnight UTC of January 1, 1970. For example, 1217646573 represents Sat Aug 2 08:39:33 2008.

How do you convert time mentioned in the Unix time format to human readable format? Perl is handy in this situation.
% perl -e 'print scalar localtime(1217646573), "\n";'

I used to work with a network monitoring software that produced logs containing time stamps in Unix time. Analyzing the logs would be difficult unless the time stamps were replaced by a human readable format.

The logs were as shown below.
STATUS [1217650382] Event: Description

Here's a perl one-liner that does the job.
% perl -pi -e 's#(?<=\[)(\d+)(?=])#scalar localtime($2)#e' /foo/bar