There might be a completely different solution. Using Sys::Mmap, you can map the entire file to a single string, and then brute-force through that string with something like while ($string =~ m/.../g) {...} (like you hinted in your post).

However, there are some caveats:

• Not all operating systems support mmap;
• you'd need a 64 bit system to fit those 12GB into your program's address space;
• I don't know how regular expressions perform with such a huge string. I've just tried it on a mmapped 200MB file (most of which consisted of \0) and it did quite well, but that's much smaller than your file.

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