$contents = "<p>no tabs here</p><p>column 1[tab]column 2</p><p>no tabs here</p>";

if ($contents =~ /<p>(.*?\[tab\].*?)<\/p>/) {
  print "yes:  ${1}\n";
} else {
  print "no\n";
}

if ($contents =~ /<p>(?=\[tab\])<\/p/) {
  print "yes:  ${1}\n";
} else {
  print "no\n";
}