I would have said the same thing that dragonchild pointed
out, i.e. that since you are matching the beginning of a line,
you can apply your regexp line by line.
However, I'll tell you something more that will save
you 30 to 50% of execution time:
Remove "use English;" and change $INPUT_RECORD_SEPARATOR
into $/. This will avoid the malicious influence
of the so called evil variables ($`, $&, $').
I have actually benchmarked your script with a few hundred
lines of logs, and this change saves about 40% of execution time on