Web Scripting: March 2010

rel="nofollow" attribute in hyperlinks to prevent comment spam and others

I faced this problem while working on a site that, a client wanted a page of his site not to be crawled and added in google's search result.
Google or other search engines, while crawling a submitted site's / existing site's page for new changes or others, they also follow links in that page and in this way the crawler notices a new page in your site.

But suppose, there is a page in your website you don't want to be crawled. Now, you may be wondering why may someone want that ? Here is an example scenario.

Problem scenario 1 :

In my specific case, the requirement was, the client had a product review module and in every product details page, there were links to "add review" like,

<a href="http://www.client_website.com/store/add_review.php?product_id=23" >Add review </a>

All the pages with different product id had the almost 99.99% the same contents in it.
And the problem was, it is causing to have like 200 pages in google with different links but the same duplicated contents. This duplicate content issue may have negative impact on the ranking of the site as it may seem that the webmaster is trying to duplicate contents and have more pages listed in search engine.

Problem scenario 2 :

I got this from here. Some spammers try to make their site more visible to search engine by spamming their site's links to the comment section of different related Blogs and Forums. You may have seen this kind of comments. This kind of SEO techniques are known as black hat techniques and if somehow the search engine understand about that a black hat technique has been used to gain a better search engine position, they even demote a site's ranking.
You may want to prevent these spamming and for doing this, all you have to do is to ensure that the spammers doesn't get benefited by their spams in your site and eventually after trying for some time, they will stop trying.

Solution :

When search engines see the attribute (rel="nofollow") on hyperlinks, those links won't get any credit when we rank websites in the search results.This isn't a negative vote for the site where the comment was posted; it's just a way to make sure that spammers get no benefit from abusing public areas like blog comments, trackbacks, and referrer lists.

About rel="nofollow"

"Nofollow" provides a way for webmasters to tell search engines "Don't follow this specific link"
or "Don't follow links on this page".

Originally, nofollow attribute appeared in the page-level meta tag, and instructed search engines not to follow / crawl any outgoing links on the page. For example:

<meta name="robots" content="nofollow" />

When nofollow was used on individual links, preventing robots from following individual links on a page required a great deal of effort (for example, redirecting the link to a URL blocked in robots.txt).
That's why the nofollow attribute value of the rel attribute was created. This gives webmasters more granular control: instead of telling search engines and bots not to follow any links on the page, it lets you easily instruct robots not to crawl a specific link. For example:

<a href="signin.php" rel="nofollow">sign in</a>

Although, this solution was quite simple It is a very important tag to use by the webmaters. That's why, I thought to share about this in my blog.

For more details and the source I used,

The Official Google Blog
Google webmaster Central
And the small video from Google Webmaster Central Channel on YouTube

reading an xml file in php and convert it into an associative array

1 comments

Today, I will write about How to read an xml file from a source url/address and convert it into an array finally so that we can parse and use it. The code is so simple if you are using php 5.0 or higher. If you don't have php 5.0 or higher, this solution below is not for you. It has another solution which involves a few more lines of code.

Let's start with an url of a xml feed. Here is the link of BBC News Front page World Edition.

http://newsrss.bbc.co.uk/rss/newsonline_world_edition/front_page/rss.xml

This page shows the latest world news in an xml feed. Now, if you want to read that front page using a php script and use those news in your website, what you should do ?

I know, there may be lots of brilliant widgets to show the latest world news to a website, But i am just taking this as an example of how to parse that xml feed and I am considering you one of the future coder of those widgets.

Here is the code.

$SimpleXML_object = simplexml_load_file("http://newsrss.bbc.co.uk/rss/newsonline_world_edition/front_page/rss.xml");   
print_r($SimpleXML_object);
echo $SimpleXML_object->channel->title ;

The above code will output something like this. This was the output at the moment I was writing this.

This magic here, it is done by a single function simplexml_load_file() which is supported from php 5. This function converts the well-formed XML document in the given file to an SimpleXMLElement object.

This xml data in SimpleXMLElement Object, you can access these data as shown in the third line of the code, $SimpleXML_object->channel->title will give you the title of the feed. You have to use the schema of the xml to get the correct data.

Now, I want to convert this SimpleXMLElement Object into an associative array. Personally, I like to deal with associative arrays rather than this Object to avoid type casting and other things.

Usually, I use the following function to do this, I like this one because, it doesn't add the attributes and I don't need that. But if you need those attributes, you may check for some other functions here. Probably, I picked the following function from this page too.

function convertXmlObjToArr( $obj, &$arr )

    {
        $children = $obj->children();
        $executed = false;
        foreach ($children as $elementName => $node)
        {
            if( @array_key_exists( $elementName , $arr ) )
            {
                if(@array_key_exists( 0 ,$arr[$elementName] ) )
                {
                    $i = count($arr[$elementName]);
                    convertXmlObjToArr ($node, $arr[$elementName][$i]);    
                }
                else
                {
                    $tmp = $arr[$elementName];
                    $arr[$elementName] = array();
                    $arr[$elementName][0] = $tmp;
                    $i = count($arr[$elementName]);
                    convertXmlObjToArr($node, $arr[$elementName][$i]);
                }
            }
            else
            {
                $arr[$elementName] = array();
                convertXmlObjToArr($node, $arr[$elementName]);   
            }
            $executed = true;
        }
        if(!$executed&&$children->getName()=="")
        {    
            $arr = (String)$obj;
        }
        return ;
    }

Usage of this function : the full code will look like this

$SimpleXML_object = simplexml_load_file("http://newsrss.bbc.co.uk/rss/newsonline_world_edition/front_page/rss.xml");
$XMLDataAraay = array();
convertXmlObjToArr($SimpleXML_object, $XMLDataAraay);
print_r($XMLDataAraay);

And now, you will be able to access the title this way. $XMLDataAraay['channel']['title']

Here, the last step of converting the Object into an Array may seem unnecessary. You can avoid this and deal directly with the object too.

And, Here is the new problem. If your site where you are going to use and extend this code to show data, this script will load the xml file every time from BBC's server. But every time, it is getting the same page unless this feed is updated in every minute.
2 problems are there I can remember of it for now,
One, it is consuming your server's valuable bandwidth and another is the slower response of fetching the file first and then processing it.

Solution : solution of this kind of problem is Caching. You can save a cache of the xml file with a suitable timeout and a timeout mechanism.. This system will save a copy of the xml file and every-time you request this file, this mechanism will look for the Cached file if the timeout interval (say, 15 minute, this means, we are expecting that this new feed will not be updated in next 15 minutes or, we can allow this maximum delay of getting that new news) of that cache file hasn't reached. If the cache file has timed out, it will refresh the cache file with new one and deliver it.

Sounds too much complex ? Actually, it is just a few lines of php code. I will discuss it some other day. :)

SQL string comparison and LIKE operator

0 comments

The original reference to this blog is from MySQL's online documentation. , msdn and another site.
There are three string comparison functions as defined in MySQL's documentation.

LIKE               Simple pattern matching
NOT LIKE     Negation of simple pattern matching
STRCMP()     Compare two strings

The description of this operator in msdn seemed more readable, that's why I am using that in my next paragraphs. For complete reference, try one of these links.

LIKE

Determines whether or not a given character string matches a specified pattern. A pattern can include regular characters and wildcard characters.

Syntax

match_expression [ NOT ] LIKE pattern [ ESCAPE escape_character ]

Arguments

match_expression

Is any valid SQL Server expression of character string data type.

pattern

Is the pattern to search for in match_expression, and can include these valid SQL Server wildcard characters.

Wildcard character	Description	Example
%	Any string of zero or more characters.	WHERE title LIKE '%computer%' finds all book titles with the word 'computer' anywhere in the book title.
_ (underscore)	Any single character.	WHERE au_fname LIKE '_ean' finds all four-letter first names that end with ean (Dean, Sean, and so on).
[ ]	Any single character within the specified range ([a-f]) or set ([abcdef]).	WHERE au_lname LIKE '[C-P]arsen' finds author last names ending with arsen and beginning with any single character between C and P, for example Carsen, Larsen, Karsen, and so on.
[^]	Any single character not within the specified range ([^a-f]) or set ([^abcdef]).	WHERE au_lname LIKE 'de[^l]%' all author last names beginning with de and where the following letter is not l.

escape_character

Is any valid SQL Server expression of any of the data types of the character string data type category. escape_character has no default and must consist of only one character.

Result Types

Boolean

Result Value

LIKE returns TRUE if the match_expression matches the specified pattern.

That's enough of the theories, Now let's have a look at some examples.

Example Queries using % wildcard

The first example that we'll take a look at involves using % in the where clause of a select statement. We are going to try to find all of the suppliers whose name begins with 'Hew'.

SELECT * FROM suppliers
    WHERE supplier_name like 'Hew%';

You can also using the wildcard multiple times within the same string. For example,

SELECT * FROM suppliers
    WHERE supplier_name like '%bob%';

In this example, we are looking for all suppliers whose name contains the characters 'bob'.

You could also use the LIKE condition to find suppliers whose name does not start with 'T'. For example,

SELECT * FROM suppliers
    WHERE supplier_name not like 'T%';

By placing the not keyword in front of the LIKE condition, you are able to retrieve all suppliers whose name does not start with 'T'.

Example Queries using _ wildcard

Next, let's explain how the _ wildcard works. Remember that the _ is looking for only one character.
For example,

SELECT * FROM suppliers
    WHERE supplier_name like 'Sm_th';

This SQL statement would return all suppliers whose name is 5 characters long, where the first two characters is 'Sm' and the last two characters is 'th'. For example, it could return suppliers whose name is 'Smith', 'Smyth', 'Smath', 'Smeth', etc.

Here is another example,

SELECT * FROM suppliers
    WHERE account_number like '12317_';

You might find that you are looking for an account number, but you only have 5 of the 6 digits. The example above, would retrieve potentially 10 records back (where the missing value could equal anything from 0 to 9). For example, it could return suppliers whose account numbers are:

123170

123171

123172

123173

123174

123175

123176

123177

123178

123179.

Example Queries using Escape Characters

Next, in Oracle, let's say you wanted to search for a % or a _ character in a LIKE condition. You can do this using an Escape character.
Please note that you can define an escape character as a single character (length of 1) ONLY.
For example,

SELECT * FROM suppliers
    WHERE supplier_name LIKE '!%' escape '!';

This SQL statement identifies the ! character as an escape character. This statement will return all suppliers whose name is %.

Here is another more complicated example:

SELECT * FROM suppliers
    WHERE supplier_name LIKE 'H%!%' escape '!';

This example returns all suppliers whose name starts with H and ends in %. For example, it would return a value such as 'Hello%'.

You can also use the Escape character with the _ character. For example,

SELECT * FROM suppliers
    WHERE supplier_name LIKE 'H%!_' escape '!';

This example returns all suppliers whose name starts with H and ends in _. For example, it would return a value such as 'Hello_'.

Redirecting cron output to a file and stop mailing

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Usually, there is an option of setting the cronjob with an email address. This email address is used to send the output of the cron script so that the developer or the system admin can check the output or use it for some other purpose.

Now, this became very annoying for me when I tried to setup a Cronjob with an interval of every minute (run in every minute), and it was sending an email to my mailbox and after a few hours my mailbox became filled up with these emails.
I want to read at these outputs later when I feel to check the output but don't want to mess with my mailbox.
So, what is the solution ?

Solution 1 : Very lame and quite obvious, use a separate address for your Cronjobs. Now a days, we can get a mailbox with almost unlimited disk access for free.

Solution 2 : This is the blog all about. Save the output of that script in a file.

Suppose, the command (here, i am talking about the comment that we usually enter while using Cpanel, please note that the command for setting up the Cronjob using SSH or Telnet is different than this) which was sending the outputs to that email was

php your_cron_script.php

Now, what we need is, use it any of the following

Use this to send the output to a file named "cron_script.log"

php your_cron_script.php >cron_script.log

The above command will create a file named "cron_script.log" if one doesn't exist or overwrite if a file with that name exists in the directory. Use the following if you want to append the output rather than overwriting the existing file.

php your_cron_script.php >>cron_script.log

These above two deals with the scripts output. But notice that it is not the error log. These commands will put the output and error information into separate files.

If you prefer to capture both output and error outputs (if any) to the same file, you can use the ?& operator to combine the two outputs. So, the command will look like,

php your_cron_script.php >>cron_script.log 2>&1

What are these 2 and 1 in 2>&1 ? These are called the file descriptors. 1 is the standard output file descriptor and 2 is the file descriptor for standard error.

So, finally, we could save and append the output of the script to a specific file in an specific folder named "cronputputs" and save (append) thestandard errors of that script to another file in an specific folder named "cronerrors" using the following command.

php your_cron_script.php >>/cronputputs/cron_script.log 2>>/cronerrors/cron_script_error.log

The above commands and more advanced options about these can be found in any book about "Shell Programming". I used Beginning Linux Programming 3rd Edition published by Wrox.(chapter 2 : Shell Programming).

php cronjob command and GET parameters

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If any reader here doesn't know what is a cronjob, for them in short, Cronjob is the scheduled job for a server to execute some command periodically in the server.
In unix server with cpanel access, usually you will find that in Advanced tad in an icon named "CronJobs"
You can execute any command and also call a php script too.

Now, to the topic what happened with me.

Problem :

While trying to make a script for cronjob, I coded the script to accept parameters in GET method.
The cron's command was like,

php /home/hosting_account/public_html/mywebsite.com/cronscript.php?sindex=VideoGames&bnode=345135031&PSPConsole=1&session_call_max=5

This command resulted into a message like,. "input file not found" .....

If this command looks unfamiliar, it is just a simple command to execute a php file from Command Line. Notice the space after php command. php is the executable's name for php and after a space next one is the php file's server absolute address.

Now, why this thing happened ? It was very foolish of me that I couldn't think about some basic ideas.

GET and POST methods are two different methods that are solely for HTTP call to a script. But here, we are writing a command that will be run exactly as we could run it from my pc's "cmd" command line.

That's why when we are writing a command, it doesn't recognize the GET parameter part of it.

So what should we do ?

Solution :

The correct command will be like,

php /home/hosting_account/public_html/mywebsite.com/cronscript.php sindex=VideoGames bnode=345135031 PSPConsole=1 session_call_max=5

Explanation : This means, every parameter should be separated by a space and when passed to the script, it is passed through the associative array $_REQUEST rather than in $_GET

So, in the script, where we would write $_GET['sindex'], we will have to write $_REQUEST['sindex']

New unnecessary problem : Now, what came to my mind that, I want this same script to be called by a cronjob and also from my browser's URL, how I we do that ?

Just add this code below at the beginning of the cron script.

            // If the $_REQUEST array has your parameters, 
            // then assign this to $_GET
            if(isset($_REQUEST['sindex']) AND $_REQUEST['bnode']){
                $_GET = $_REQUEST ;
            }

But, this solution's code needs to be changed to check the correct parameter. But, more generic solution will be,

            if(isset($_REQUEST[$_SERVER['argv']['0']])){
                $_GET = $_REQUEST ;
            }

I has been a long discussion for this simple thing, So, I am not going to explain this last code ;)

how to calculate script's execution time in php

0 comments

Many times, we need to check what was the execution time for a script we have written in PHP. This was necessary for me when I was requesting some data using an API and the execution time of each api call needs to be traced.
We need to take care of the execution time (minimize it) to ensure that the script is not Timed Out in the server.
Doing this is quite simple.
Just a php function microtime( ) is enough to do this.

Here is the example :

$start_time = microtime(true);
// Do some work or your whole script
$end_time = microtime(true);
$execution_time = $end_time - $start_time ;

Now, the function's details

microtime
(PHP 4, PHP 5)

microtime — Return current Unix timestamp with microseconds

Description

mixed microtime ([ bool $get_as_float ] )

microtime() returns the current Unix timestamp with microseconds. This function is only available on operating systems that support the gettimeofday() system call.

Parameters

get_as_float

When called without the optional argument, this function returns the string "msec sec" where sec is the current time measured in the number of seconds since the Unix Epoch (0:00:00 January 1, 1970 GMT), and msec is the microseconds part. Both portions of the string are returned in units of seconds.

If the optional get_as_float is set to TRUE then a float (in seconds) is returned.

And now, here is an Object Oriented approach of doing this
example :

    $timer = new Timer();
    $timer->start();
    //   Add the codes whose time you need to count 
    $timer->stop();
    echo "elapsed time ".$timer->getTime() ;  // Use method    getTime()   to get the elapsed time in seconds
    $timer>printTime();                      // Use printTime()   to  echo the elapsed time 
                                             //like, Elapsed Time : 0.0893499851227 seconds
    
//And, here is the class : 
class Timer {
    var $clock = 0;
    var $elapsed = 0 ;

    function start () {
        $this->clock = microtime(true);
        $this->elapsed = 0 ;
        return true ;
    }

    function stop () {
        if($this->clock == 0) return false ;       
        $this->elapsed = microtime(true) - $this->clock ;
        return true ;
    }
    
    function getTime(){
        return $this->elapsed ;
    }
    
    function printTime(){
        if($this->elapsed != 0){
            $txt = "Elapsed Time : " . $this->elapsed . "  seconds";
        }else if($this->clock == 0){
            $txt = "Counter Not started yet";
        }else{
            $txt = "Counter started but Not stopped";
        }
        echo "
".$txt."
";
        return $txt ;
    }
}

Javascript page Redirection

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Maybe, you have seen while browsing internet this thing. When a form has been submitted successfully, in the webpage, there is some text like saying,

Update Successful, You will be redirected after 5 seconds. If you are not redirect automatically, please click in this link to redirect.

or,

This site has been moved to a new domain, You will be redirected after 5 seconds.

The later message is shown when the website has been moved to a new domain name and you need to redirect the user,

Now, how it's done

Here is the sample script to do this

<html>
<head>
<script type="text/javascript">

</script>
</head>
<body onLoad="setTimeout('delayer()', 5000)">

<h2>Prepare to be redirected!</h2>
<p>This page is a time delay redirect, please update your bookmarks to our new
location!</p>

</body>
</html>

Now, the explanation of this code fragment 
When the page is loaded, the onLoad event executes this script 

setTimeout('redirect()', 5000)
It sets a timeout after 5000 miliseconds / 5 seconds and after 5 seconds, the function redirect is called. In the function redirect, this window's location property is changed and this window is redirected to http://new-domain.com 

The setTimeout() Method
Syntax
   var t=setTimeout("javascript statement",milliseconds);
The setTimeout() method returns a value - In the statement above, the value is stored in a variable called t. If you want to cancel this setTimeout(), you can refer to it using the variable name.

The first parameter of setTimeout() is a string that contains a JavaScript statement. This statement could be a statement like "alert('5 seconds!')" or a call to a function, like "redirect()".

The second parameter indicates how many milliseconds from now you want to execute the first parameter.

Note: There are 1000 milliseconds in one second.

Window Object  
The window object represents an open window in a browser.
window.location  : Returns the Location object for the window

Web Scripting

rel="nofollow" attribute in hyperlinks to prevent comment spam and others

About rel="nofollow"

reading an xml file in php and convert it into an associative array

SQL string comparison and LIKE operator

Syntax

Arguments

Result Types

Result Value

Redirecting cron output to a file and stop mailing

php cronjob command and GET parameters

how to calculate script's execution time in php

Javascript page Redirection

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