$doc =~ s/(?:\[|\]|\')//g   -->  $doc =~ s/[\[\]\']//g
$doc =~ s/(?:\[|\]|\')+//g  -->  $doc =~ s/[\[\]\']+//g

##</code><code>##

use 5.16.2;
use warnings;

my $doc = "'C-3PO' or 'See-Threepio' is a humanoid robot character from the [[Star Wars]] universe who appears in the original ''Star Wars'' films, the prequel trilogy and the sequel trilogy.\n";
$doc =~ s/(?:\[\[|\]\]|'')//g; # Only replace doubles, to make sequence longer than a single character
say $doc;

$doc =~ "'C-3PO' or 'See-Threepio' is a humanoid robot character from the [[Star Wars]] universe who appears in the original ''Star Wars'' films, the prequel trilogy and the sequel trilogy.\n";
$doc =~ s/[\[\]']//g; # set based replacement
say $doc;