Archive for May, 2010

Using the ‘date’ command in your crontab

Crontab, as most people know, enables users to schedule commands or shell scripts to run periodically at certain times or dates.

The other day, this very useful Linux tool gave me a hard time! πŸ™
Indeed, one of my commands wasn’t working in cron but was working perfectly fine when written in a shell console.

The faulty command looked like this:

0 5 * * 3 /data/script.sh > /data/script_`date +%y%m%d`.log 2>&1

If I run this command in a shell console, everything works fine and I get a log file containing today’s date in its filename. However, if I set this command line in my crontab, it doesn’t work and no log file is even created!

Reading the documentation of cron, I discovered the following statement:

Percent-signs (%) in the command, unless escaped with backslash (\), will be changed into newline characters, and all data after the first % will be sent to the command as standard input.

Well, this is good to know, isn’t it? πŸ˜‰
We need to escape the percent-signs on our command line.

So in order to get our ‘faulty’ command to run in cron, it needs to look like the following:

0 5 * * 3 /data/script.sh > /data/script_`date +\%y\%m\%d`.log 2>&1

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Validate your EAN barcode

On one of the applications I am working on, I had to validate an EAN (European Article Number) barcode.
This application is mostly using JavaScript validation so I asked my friend Google to find me a JavaScript method which would check my EAN barcode.
It found validators in different languages but none in JavaScript. πŸ™

Because one is never better served than by oneself, I decided to write it myself and share it with you. πŸ˜‰

function checkEan(eanCode) {
	// Check if only digits
	var ValidChars = "0123456789";
	for (i = 0; i < eanCode.length; i++) { 
		digit = eanCode.charAt(i); 
		if (ValidChars.indexOf(digit) == -1) {
			return false;
		}
	}
	
	// Add five 0 if the code has only 8 digits
	if (eanCode.length == 8 ) {
		eanCode = "00000" + eanCode;
	}
	// Check for 13 digits otherwise
	else if (eanCode.length != 13) {
		return false;
	}
	
	// Get the check number
	originalCheck = eanCode.substring(eanCode.length - 1);
	eanCode = eanCode.substring(0, eanCode.length - 1);
	
	// Add even numbers together
	even = Number(eanCode.charAt(1)) + 
	       Number(eanCode.charAt(3)) + 
	       Number(eanCode.charAt(5)) + 
	       Number(eanCode.charAt(7)) + 
	       Number(eanCode.charAt(9)) + 
	       Number(eanCode.charAt(11));
	// Multiply this result by 3
	even *= 3;
	
	// Add odd numbers together
	odd = Number(eanCode.charAt(0)) + 
	      Number(eanCode.charAt(2)) + 
	      Number(eanCode.charAt(4)) + 
	      Number(eanCode.charAt(6)) + 
	      Number(eanCode.charAt(8)) + 
	      Number(eanCode.charAt(10));
	
	// Add two totals together
	total = even + odd;
	
	// Calculate the checksum
    // Divide total by 10 and store the remainder
    checksum = total % 10;
    // If result is not 0 then take away 10
    if (checksum != 0) {
        checksum = 10 - checksum;
    }

	// Return the result
	if (checksum != originalCheck) {
		return false;
	}
	
    return true;
}

Note that this code can validate EAN-8 and EAN-13 barcodes.

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The message tags of MyFaces and RichFaces

Working on an application using MyFaces and RichFaces, I had no choice but understand what is the difference between the message tag provided by Myfaces (h:message) and the message tag overridden by RichFaces (rich:message).

These tags allow to display information about the first FacesMessage that is assigned to the component referenced by the “for” attribute. The difference is that the RichFaces tag has some extra functionalities such as Ajax rendering, error markers and predefined css class names.
Have a look at the following page for more details: http://livedemo.exadel.com/richfaces-demo/richfaces/message.jsf

This is all nice and well but it is not the only difference. Indeed, the HTML code generated by both these frameworks will also be different!

First of all, let’s see how the tag <h:message styleClass="errormsg" for="element"/> will be transformed. If there is no message to display, nothing will be generated (which is a good behaviour). However, if a message is present, the tag will be replaced by the following HTML code:

<span class="errormsg">Required.</span>

So far, so good!

But now let’s check what code RichFaces is generating for the tag <rich:message styleClass="errormsg" for="element"/>.
The following is the code created if there is NO message to render:

<span class="rich-message errormsg" id="form:j_id255">
    <span class="rich-message-label"></span>
</span>

And here is the code which will replace the RichFaces tag if there is a message to display:

<span class="rich-message errormsg" id="form:j_id255">
    <span class="rich-message-label">Required.</span>
</span>

As you can see, the main difference is that RichFaces is wrapping the original span tag into another span tag. But, it is also generating some code even if there is no message to display! You would ask why is it doing that? The response is simple. The wrapper span element is necessary for RichFaces to Ajax-render the message tag if an error message has to be displayed for the targeting element.

So make sure you don’t put any padding or margin style in your custom CSS class which I called ‘errormsg’ in my example. Otherwise, you might have a gap when you were expecting nothing… (this happened to me) πŸ˜‰

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