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Convert Date TimeZone in Apache Server Log

Recently, I helped a user who was given the task of converting the dates in a Apache server log from GMT (Greenwich Mean Time) to PST (Pacific Standard Time). In theory all that is necessary is to extract the date/time string from each log entry line, subtract 7 or 8 hours depending on whether daylight savings time is in force or not, and rebuild the log entry line with the new date/time string. On first examination, this would seen to be an easy task which would be suitable for gawk given that it has support for mktime and strptime. However