$match = '(foo|baz|bar)';

while (<INPUT>) {
   next if ($_ !~ /$match/o);
}

##</code><code>##

$m_1 = '(bar|baz|foo)';
$m_2 = '([Bb]lah|[Cc]ore)';
$m_3 = '(root|sys|user)';

while (<INPUT>) {
   next if ($_ !~ /$m_1/o);

   chomp($line = $_);

   if ($line =~ /$m_2/o && $something) {
      &func("param");

   } elsif ($line =~ /$m_3/o && $something_else) {
      &other("var");
   }
}