my $oldhostname = "whatever";
my $newhostname = shift || "somethingnew";
die "Nothing to do\n" if ( $oldhostname eq $newhostname );

print "changing $oldhostname to $newhostname\n";
open( FLIST, "<file_containing_list_of_filenames" ) or
    die "Unable to get list of file names to personalize\n";

my @oldfiles = <FLIST>;
chomp @oldfiles;

my @renamefiles = grep /$oldhostname/i, @oldfiles;
s/$oldhostname/$newhostname/gi for @renamefiles;

for my $file ( @oldfiles ) {
    my $newfile = ( $file =~ /$oldhostname/i ) ?
          shift @renamefiles : "$file.tmp";
    open(IN, "<$file") or die "Unable to read $file: $!\n";
    open(OUT, ">$newfile) or die "Can't write $newfile:$!\n;
    while (<IN>) {
        s/$oldhostname/$newhostname/gi;
        print OUT;
    }
    close OUT;
    close IN;
    unlink $file;
    rename $newfile, $file if ( $newfile eq "$file.tmp" );
}