All of those alternations are possibly causing the regex engine to do a lot of extra work due to backtracking.

Consider changing the parts of your regexp that look like 

(?:a|b|c)

[download]

to use independent subexpressions like 

(?>a|b|c)

[download]

This is documented in perlre - Extended Patterns (look for (?>pattern) - it's a fair way down that section).

You may also find Regexp::Debugger to be a useful tool for visualising what the regex engine is doing.

-- Ken

In reply to Re: Help with speeding up regex by kcott
in thread Help with speeding up regex by eversuhoshin

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