use Path::Tiny qw/ path /;
path( $newFileName )->spew_utf8( qq{<base href="$insert_str">}, $content  );

##</code><code>##

$ 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;">