G'day xnous,

Welcome to the Monastery.

Please follow the advice already given by ++hippo. In addition to representative input data, show the expected output data. Also, tell us what Perl version you're using: features in more recent Perls may improve performance.

Here's some very general advice:

• Have a read of "perlperf: Perl Performance and Optimization Techniques". Your basic steps should generally be: get the code working; profile to find areas of poor performance; benchmark to see if improvements are really improvements — you'll probably need multiple iterations of some, or all, of these steps.
• Reading all records into an array, then reading them all again from that array, is effectively doing the work twice. Instead, read the records from the file and process them immediately. Making a backup of the original file first, is advisable.
• The performance of regexes can often be improved if they include anchors; e.g. ^, $, \b, \b{}, and so on — see "perlrebackslash: Perl Regular Expression Backslash Sequences and Escapes" for details.
• Use Regexp::Debugger to test individual regex patterns. I use this module a lot and often find places where I can make improvements; for instance, by eliminating backtracking.

When you provide the requested code and data, more specific advice will likely be possible.

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