Yes, two handles at once, like so:

open(DB_RESULT,">/path/to/result/db/file");
open(DB_SRC,"/path/to/source/db/file");
while (<DB_SRC>){
  if($_ ~= /$user/){
    my @user_fields = split /:/,$_;
    $user_fields[2] = $user_fields[2] + $newtraffic; 
    my $newline = $user_fields[0].':'.$user_fields[1].':'.$user_fields
+[2];
    print DB_RESULT, $newline;
  } else {
    print DB_RESULT, $_;
  }
}
close(DB_SRC);
close(DB_RESULT);
my $result = `mv /path/to/result/db/file /path/to/source/db/file`;
[download]

There may be some slick way to do this with only one file open overwriting only the line you are concerned with, but it is not apparent to me at this late hour. And generally I am of the mind that it is more important to ensure that a program works than that it is fast or fancy.

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