You may have to forgo the single-line command, and do something akin to this (which is not tested)

use strict;
use warnings;

my $newfolder = shift(@ARGV);

use Tie::File;  

use Fcntl 'O_RDWR';

chdir($newfolder);

my @list=glob("*");

foreach my $file (@list){

tie @array, 'Tie::File', $file, mode => O_RDWR or die "could not tie $
+file because...$!\n"

foreach my $record (@array) {
 $record =~ s/$oldword/$newword/ig;
}
}
[download]

Read docs on Tie::File; it will probably help.

Also, read up on glob.