use File::Copy;

open ( my $s, "<", "source" ) or die "Could not open source file: $!\n";
open ( my $d , ">>", "dest" ) or die "Could not open destination file : $!\n";

copy($s, $d) or die "Could not copy source to dest : $!\n";

(close $s && close $d ) or die "Could not close file handles : $!\n";