$NetPattern = qr{mbist[\w+\d+\/]*\[\d+\]}x;
if ($NetName =~  $NetPattern) {# Do fantastical things...}

##</code><code>##

$NetPattern = 'mbist[\w+\d+\/]*\[\d+\]';
if ($NetName =~ qr/$NetPattern/x) {# Do fantastical things...}

##</code><code>##

$NetPattern = 'mbist[\w+\d+\/]*\[\d+\]';
if ($NetName =~ m/$NetPattern/x) {# Do fantastical things...}