RaiseError

    local $dbh->{RaiseError} = 'on';
    local $dbh->{PrintWarn}  = 'off';
    local $dbh->{PrintError} = 'off';

    eval {
	$sth_ins->execute( $hd, $sz, $mtime, $_, $File::Find::dir, $dir );
	warn( "Added: ", $hd, " ", $mtime, " ", iso8601date($ctime), " ", $File::Find::name, "\n" )
	  if $verbose > 1;
	$new++;
    };

    if ( $@ ) {
	if ( $@ =~ /duplicate key.*"iuniq"/ ) {
	    $dup++;
	}
	else {
	    warn($@);
	}
    }

RESULT:

DBD::Pg::st execute failed: ERROR:  duplicate key violates unique constraint "iuniq" at bin/mkindex line 161.
Added: ...