in reply to Defensive Programming and Audit Trails
Just to expand upon the concept of making the log file easy to parse, it should be emphasized that certain date formats (e.g. ISO 8601 format) are easily parseable by some common Date and Time modules. In particular, I'm thinking of HTTP::Date, though there are plenty of others, depending on what sort of format you prefer.
So, when you pick a log file format, give the timestamps you use some thought, and be sure they're consistent.
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