Hi,

#TODO Replace all of the links with fully qualified url's
#TODO Save the master_content to a file with the same file name

Here you go

use Path::Tiny qw/ path /;
path( $newFileName )->spew_utf8( qq{<base href="$insert_str">}, $conte
+nt  );
[download]

You might need to html-escape $insert_str ... could use Mojo for that part

$ perl -Mojo -e " $dom = x(q{<base>}); $dom->at(q{base})->attr(qw{href
+ http://example.com/?&}); print $dom "
<base href="http://example.com/?&amp;">
[download]

See Path::Tiny, https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base, https://metacpan.org/pod/ojo#x