my $infile  = 'in.tmp';
    my $outfile = 'out.tmp';
    open(my $fhin,  '<', $infile)  or die "error: open '$infile': $!";
    open(my $fhout, '>', $outfile) or die "error: open '$outfile': $!";
    while (my $line = <$fhin>) {
       $line =~ s/\bPeking\b/Beijing/g;
       print $fhout $line;
    }
    close($fhin);
    close($fhout);