open(FILE,"dumptape.log") ||
  die ("Could not open file: $!");

my $success;
for ( $success = 0; $success != 1 && <FILE>; ) {
  if ( /Dump phase number 3/ ) {
    print <FILE>;
    $success = 1;
  }
}

close ( FILE );
if ( !$success ) {
  print "Failed dump log\n"; 
  #do other failed dump log stuff here
}