Reduce redundant logfile

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http://unix.stackexchange.com – I often have longer redundant log files, redundant in the sense that blocks of text repeat with minor changes. The length of the files makes it difficult to spot the actual information. I had the idea to write a script which identifies recurrences and reduces the file by replacing each recurrence by the output of diff for consecutive blocks. Before I start I would like to know if such a tool (or maybe option to diff) already exists. (HowTos)