oshalla and eight-one gave good descriptions of the grep block

The code almost works. Here are a couple of mods to make things work

The variable $file requires a my declaration

'mv' is not a native perl function, use rename file1, file2. You could also use system() but, on my computer, that function seemed to work a little slower

You need to put double quotes around the second file otherwise perl interprets the '.' as the concatenation operator

Here is the modified code

#! /usr/local/bin/perl

use strict;
use warnings;
use diagnostics;

die unless chdir "/path/directory";
die unless opendir DIR, '.';
foreach my $file (grep {-f && (14 < -M)} readdir DIR) {
#    print $file,"\n";
    rename $file, ".$file";
#    system("mv", $file, ".$file");
}
closedir DIR;
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