use File::Slurp;

if($msg =~ /(.*)\+\+/) {
  my $user = $1;

  my @lines = split m[$/], read_file ($karma_file);

  # Set @data to all lines not starting with $user,
  # setting $user_line as the last line starting
  # with $user as a side-effect.  Note that do{}
  # returns the value of the last expression executed,
  # so the 0 is required.
  my $user_line = "";
  my @data = grep { /^$user/ ? do{$user_line = $_;0} : 1 } @lines;

  # We already have $user, and redeclaring it causes a warning.
  # So, instead, we just skip it.
  my (undef, $karma) = split /\s/, $user_line;
  ++$karma;
  push @data, "$user $karma";

  overwrite_file($karma_file, @data);
}