Use a more straightforward return style in script rules. Instead of

	if cond then
		return true
	else
		return false
	end

just do

	return cond

scripts/auth-owners.nse

@@ -30,16 +30,10 @@ portrule = function(host, port)
 	local auth_port = { number=113, protocol="tcp" }
 	local identd = nmap.get_port_state(host, auth_port)
 
-	if
-		identd ~= nil
+	return identd ~= nil
 		and identd.state == "open"
 		and port.protocol == "tcp"
 		and port.state == "open"
-	then
-		return true
-	else
-		return false
-	end
 end
 
 action = function(host, port)

scripts/banner.nse

@@ -26,7 +26,7 @@ local stdnse = require "stdnse"
 ---
 -- Script is executed for any TCP port.
 portrule = function( host, port )
-  return (port.protocol == "tcp" and true) or false
+  return port.protocol == "tcp"
 end
 
 

scripts/dns-random-txid.nse

@@ -1,4 +1,3 @@
-
 description = [[
 Checks a DNS server for the predictable-TXID DNS recursion
 vulnerability.  Predictable TXID values can make a DNS server vulnerable to

scripts/mysql-info.nse

@@ -108,19 +108,12 @@ end
 portrule = function(host, port)
 	local extra = port.version.extrainfo
 
-	if
-		(port.number == 3306
-		or port.service == "mysql")
+	return (port.number == 3306 or port.service == "mysql")
 		and port.protocol == "tcp"
 		and port.state == "open"
 		and not (extra ~= nil
 			and (extra:match("[Uu]nauthorized")
 				or extra:match("[Tt]oo many connection")))
-	then
-		return true
-	end
-
-	return false
 end
 
 action = function(host, port)

scripts/nbstat.nse

@@ -51,18 +51,12 @@ hostrule = function(host)
 	local port_u137 = nmap.get_port_state(host,
 		{number=137, protocol="udp"})
 
-	if (
-		(port_t135 ~= nil and port_t135.state == "open") or
+	return (port_t135 ~= nil and port_t135.state == "open") or
 		(port_t139 ~= nil and port_t139.state == "open") or
 		(port_t445 ~= nil and port_t445.state == "open") or
 		(port_u137 ~= nil and
 			(port_u137.state == "open" or
-			port_u137.state == "open|filtered")))
-	then
-		return true
-	else
-		return false
-	end	
+			port_u137.state == "open|filtered"))
 end
 
 

scripts/smb-check-vulns.nse

@@ -42,15 +42,7 @@ require 'smb'
 require 'stdnse'
 
 hostrule = function(host)
-
-	local port = smb.get_port(host)
-
-	if(port == nil) then
-		return false
-	else
-		return true
-	end
-
+	return smb.get_port(host) ~= nil
 end
 
 local VULNERABLE = 1

scripts/smb-enum-domains.nse

@@ -53,15 +53,7 @@ require 'smb'
 require 'stdnse'
 
 hostrule = function(host)
-
-	local port = smb.get_port(host)
-
-	if(port == nil) then
-		return false
-	else
-		return true
-	end
-
+	return smb.get_port(host) ~= nil
 end
 
 action = function(host)

scripts/smb-enum-sessions.nse

@@ -52,15 +52,7 @@ require 'smb'
 require 'stdnse'
 
 hostrule = function(host)
-
-	local port = smb.get_port(host)
-
-	if(port == nil) then
-		return false
-	else
-		return true
-	end
-
+	return smb.get_port(host) ~= nil
 end
 
 ---Attempts to enumerate the sessions on a remote system using MSRPC calls. This will likely fail 

scripts/smb-enum-shares.nse

@@ -72,15 +72,7 @@ require 'smb'
 require 'stdnse'
 
 hostrule = function(host)
-
-	local port = smb.get_port(host)
-
-	if(port == nil) then
-		return false
-	else
-		return true
-	end
-
+	return smb.get_port(host) ~= nil
 end
 
 ---Attempts to enumerate the shares on a remote system using MSRPC calls. This will likely fail 

scripts/smb-enum-users.nse

@@ -124,15 +124,7 @@ require 'smb'
 require 'stdnse'
 
 hostrule = function(host)
-
-	local port = smb.get_port(host)
-
-	if(port == nil) then
-		return false
-	else
-		return true
-	end
-
+	return smb.get_port(host) ~= nil
 end
 
 ---Attempt to enumerate users through SAMR methods. See the file description for more information. 

scripts/smb-os-discovery.nse

@@ -31,15 +31,7 @@ require 'stdnse'
 
 --- Check whether or not this script should be run.
 hostrule = function(host)
-
-	local port = smb.get_port(host)
-
-	if(port == nil) then
-		return false
-	else
-		return true
-	end
-
+	return smb.get_port(host) ~= nil
 end
 
 --- Converts numbered Windows version strings (<code>"Windows 5.0"</code>, <code>"Windows 5.1"</code>) to names (<code>"Windows 2000"</code>, <code>"Windows XP"</code>). 

scripts/smb-security-mode.nse

@@ -60,15 +60,7 @@ require 'smb'
 
 -- Check whether or not this script should be run.
 hostrule = function(host)
-
-	local port = smb.get_port(host)
-
-	if(port == nil) then
-		return false
-	else
-		return true
-	end
-
+	return smb.get_port(host) ~= nil
 end
 
 

scripts/smb-server-stats.nse

@@ -39,15 +39,7 @@ require 'smb'
 require 'stdnse'
 
 hostrule = function(host)
-
-	local port = smb.get_port(host)
-
-	if(port == nil) then
-		return false
-	else
-		return true
-	end
-
+	return smb.get_port(host) ~= nil
 end
 
 action = function(host)

scripts/smb-system-info.nse

@@ -55,15 +55,7 @@ require 'smb'
 require 'stdnse'
 
 hostrule = function(host)
-
-	local port = smb.get_port(host)
-
-	if(port == nil) then
-		return false
-	else
-		return true
-	end
-
+	return smb.get_port(host) ~= nil
 end
 
 ---Retrieves the requested value from the registry. 

scripts/smtp-strangeport.nse

@@ -17,21 +17,10 @@ license = "Same as Nmap--See http://nmap.org/book/man-legal.html"
 categories = {"malware"}
 
 portrule = function(host, port) 
-	if 
-		(	port.number ~= 25
-			and
-			port.number ~= 465
-			and
-			port.number ~= 587
-			and 
-			port.service == "smtp" )
+	return port.service == "smtp" and
+		port.number ~= 25 and port.number ~= 465 and port.number ~= 587
 		and port.protocol == "tcp" 
 		and port.state == "open"
-	then
-		return true
-	else
-		return false
-	end
 end
 
 action = function()

scripts/sniffer-detect.nse

@@ -17,14 +17,11 @@ categories = {"discovery"}
 
 -- okay, we're interested only in hosts that are on our ethernet lan
 hostrule = function(host, port)
-	if host.directly_connected == true and
-	   host.mac_addr ~= nil and
-	   host.mac_addr_src ~= nil and
-	   host.interface ~= nil and
-	   nmap.get_interface_link(host.interface) == 'ethernet' then
-	    return true
-	end
-	return false
+	return host.directly_connected == true and
+		host.mac_addr ~= nil and
+		host.mac_addr_src ~= nil and
+		host.interface ~= nil and
+		nmap.get_interface_link(host.interface) == 'ethernet'
 end
 
 --[[