I think the OP wanted all lines before the last instance of the TIMESTAMP match, including non-matching ones.

Better maybe as: 


my @log_final;
my $watching_for_last_match = 0;
#  ^ Bonus! This var will give a count of 
#    entries within the timestamp at the end,
#    compare with scalar(@log_final) for stats

while (my $log_line = $log_bckwards->readline) {
  if ( $watching_for_last_match ) {    
    if ($log_line !~ /$TIMESTAMP/) {
      last;
    }
  } else {
    if ($log_line =~ /$TIMESTAMP/) {
      $watching_for_last_match++;
    }
  }        
  unshift @log_final, $log_line;
}

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In reply to Re^2: Store log file content from EOF till final occurrence of timestamp by 1nickt
in thread Store log file content from EOF till final occurrence of timestamp by jayu_rao

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