This gives you the output you're looking for: 
use warnings;
use strict;

while (my $match = <DATA>) {
    $match =~ /event="([^(]+).*"/;
    print "$1\n";
}

__DATA__
<ID="user_one" event="open(2)">
<ID="user_one" event="system booted">
<ID="user_one" event="init(1m)">

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In reply to Re: Help with this simple regex by toolic
in thread Help with this simple regex by cspctec

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