I could attempt to explain this, but someone has already done a very good job of this, so I’d rather just provide a link to their content. The post is from the author of “High Performance MySQL”, Baron Schwartz, and covers writing an SQL Exclusion Join. The key area of interest is the section on LEFT OUTER joins. He offers this example query:

SELECT apples.Variety
FROM apples
    LEFT OUTER JOIN oranges
        ON apples.Price = oranges.Price
WHERE oranges.Price IS NULL

When in doubt, find someone smarter to answer the question for you. Thanks Baron!

function preprint($arr){
  echo '< pre>'.print_r($arr).'< /pre>';
}
$array = scandir(getcwd());
preprint($array); // nicely formatted display of the array

 
Of course, you can skip the print/echo portion if you don’t wish to display the contents and just use the array to perform other checks, but you get the idea.

function strtotimefix($val,$timestamp=0){
	if ($timestamp==0){ $timestamp = time(); }
	if (date('m') == date('m',strtotime('-1 month'))){
		$timestamp = strtotime('-3 days',$timestamp);
	}else{
		$timestamp = time();
	}
	$strtotime = strtotime($val,$timestamp);
	return $strtotime;
}

So what’s happening? Basically, the function will check if the numeric month is the same between the current month and the month through ‘-1 month’. If so, it subtracts 3 days from the current timestamp, then runs through the strtotime function using the new timestamp. If everything is fine, nothing is altered, so you don’t have to worry that using the strtotimefix() function will break a perfectly normal strtotime(‘-1 month’) call. Be advised that if you are not doing a call with ‘-x month’, the function will return an incorrect timestamp by 3 days (I hope to update it to be self-aware and only ‘fix’ when the bug would be introduced).

Updated on March 30, 2010:
Changed it to -3 days to deal with February/March.

• A copy of the PHP book with a tab on pages 149 and 150 for common RegEx syntax
• A link to RegExPal, a color coding Regular Expression tester.

Common Regular Expressions:

Date and Time RegEx

Time format (no seconds):
HH:MM am/pm

^([1-9]|1[012]):(0[0-9]|[1-5][0-9])\s?(am|AM|pm|PM)$

Date in mm/dd/yyyy format, with an option for m/d/yyyy (exclude zero’s)

^(0?[1-9]|1[012])[ \/.-](0?[1-9]|[12][0-9]|3[01])[ \/.-](19|20)\d\d$

Date in dd/mm/yyyy format, with an option for d/m/yyyy (exclude zero’s)

^(0?[1-9]|[12][0-9]|3[01])[ \/.-](0?[1-9]|1[012])[ \/.-](19|20)\d\d$

Demographics RegEx

Age in years – max 122

^([0-9]|[1-9][0-9]|[1-9][0-1][0-9]|[1-9]2[0-2])$

Height in Feet and Inches:
6’3″

^([1-8]')?\s?([1-9]|1[01])$

Contact Information RegEx

U.S. Phone Number – parenthesis, periods, dashes, and spaces are allowed:
(123) 456.7890

^((\(\d{3}\)\s?|\d{3}\.)|(\d{3}[-\s\.]))?\d{3}[-\s\.]\d{4}$

U.S. Zip Code – 5 or 9 digit with dash

^\d{5}([\-]\d{4}){0,1}$

Email Address – (use preg_match) credit goes to fightingforalostcause.net

/^[-_a-z0-9\'+*$^&%=~!?{}]++(?:\.[-_a-z0-9\'+*$^&%=~!?{}]+)*+@(?:(?![-.])[-a-z0-9.]+(?<![-.])\.[a-z]{2,6}|\d{1,3}(?:\.\d{1,3}){3})(?::\d++)?$/iD

Currency RegEx

Currency – U.S. Dollars and Cents with commas for multiple’s of 1000 and a period for the decimal:
$12,000.23

^\$?([1-9]{1}[0-9]{0,2}(\,[0-9]{3})*(\.[0-9]{0,2})?|[1-9]{1}[0-9]{0,} (\.[0-9]{0,2})?|0(\.[0-9]{0,2})?|(\.[0-9]{1,2})?)$

Currency – British Pounds with commas for multiple’s of 1000 and a period for the decimal:
£12,000.23

^\u00A3?([1-9]{1}[0-9]{0,2}(\,[0-9]{3})*(\.[0-9]{0,2})?|[1-9]{1}[0-9]{0,} (\.[0-9]{0,2})?|0(\.[0-9]{0,2})?|(\.[0-9]{1,2})?)$

Currency – Euros with periods for multiple’s of 1000 and a comma for the decimal:
€12.000,23

^\u20AC?([1-9]{1}[0-9]{0,2}(\.[0-9]{3})*(\,[0-9]{0,2})?|[1-9]{1}[0-9]{0,} (\,[0-9]{0,2})?|0(\,[0-9]{0,2})?|(\,[0-9]{1,2})?)$

Currency – Euros, French style, with spaces for multiple’s of 1000 and a comma for the decimal:
€12 000.23

^\u20AC?([1-9]{1}[0-9]{0,2}(\s[0-9]{3})*(\,[0-9]{0,2})?|[1-9]{1}[0-9]{0,} (\,[0-9]{0,2})?|0(\,[0-9]{0,2})?|(\,[0-9]{1,2})?)$

Here is a quick screenshot of some of the highlighting in action:

Be advised that this is based on JavaScript regular expressions, which are comparable to the PERL compatible RegEx functions, such as preg_replace() and preg_match(). It’s a good idea to get familiar with this syntax, as ereg() and eregi() style functions will be removed from PHP6 when it is released, sometime in the future. Make sure to also checkout the Regular Expressions Cookbook contributed to by the author of RegExPal.com.

This tip is courtesy of a great article, 10 Advanced PHP Tips Revisited

When referencing an array’s value via a numeric key, you follow the variable name ($variable) with the numeric index, enclosed by square brackets [5]. e.g. $variable[5] = ‘value’
However, when $variable represents a string, using the same syntax will return a string with the character at the position specified by the numeric index (0 marks the first character in the $variable string). An example:

$string = 'abcdefg';
var_dump($string[2]);

Output: string(1) “c”

Where this comes into play is when using isset() rather than strlen(). Consider the following example:

$string = 'abcdefg';
if (isset($string[5])){
  echo $string[5].' found!';
}

Output: f found!

$string = 'abcdefg';
if (isset($string[7])){
     echo $string[7].' found!';
  }else{
     echo 'No character found at position 7!';
}

Output: No character found at position 7!

This is faster than using strlen() because, “… calling a function is more expensive than using a language construct.” It’s little tricks like this that will keep your code lean and efficient. Thanks to Chris Shiflett and Sean Coates for their contributions to the referenced article.

http://www.phpreferencebook.com/?variable=value&name=Mario%20Lurig&gender=male%21

or

http://www.phpreferencebook.com/?variable=value&name=Mario Lurig&gender=male!

1. Display the whole string (everything after the question mark)

• <?php echo $_SERVER['QUERY_STRING']; ?>

• variable=value&name=Mario%20Lurig&gender=male

2. Display the whole string decoded (convert %## to original characters)

• <?php echo urldecode($_SERVER['QUERY_STRING']); ?>

• variable=value&name=Mario Lurig&gender=male!

3. Show each variable and value as an array (already decoded)

• <?php print_r($_GET); ?>

• Array ( [variable] => value [name] => Mario Lurig [gender] => male!

• <?php echo '<pre>'; print_r($_GET); echo '< /pre>'; ?>

• Array
  (
      [variable] => value
      [name] => Mario Lurig
      [gender] => male!
  )
  

There are lots of options from there, so don’t let this be the end of your exploration of how to display a query string value on a page. If you have any great tricks, feel free to share them in the comments below!

allowed_tags – [optional] $string

Remove HTML tags and comments from $string. If specific tags should be
excluded, they can be specified inside allowed_tags.

Examples:
$string = "<p>This is a paragraph. </p><strong>Yay!</strong>";
echo strip_tags($string), strip_tags($string, '<p>');

HTML Source Code:

This is a paragraph. Yay! <p>This is a paragraph. </p>Yay!

$string = "I <strong>love</strong> this book because it costs <$20.";
echo strip_tags($string);

HTML Source Code:

I love this book because it costs

As you can see, it removed the <$20 portion of the string as well, even without the closing greater than ( > ) tag at the end. Be careful when using strip_tags(), especially without specifying the allowed tags, or consider using an alternate such as htmlspecialchars() to encode the characters into their html equivalent rather than removing them.

error_reporting(E_ALL);
ini_set('display_errors', '1');

Now, continue to beat your head against your keyboard while you continue to hunt down your missing semicolon or closing parenthesis.

• \n – new line
• \r – carriage return
• \t – tab
• \b – backspace

But many wonder when to use them or more specifically, why they aren’t working as expected. So let’s address the basic usage and rules.

Rule #1: When using a formatting character in your code, it must be within “double quotations” otherwise it will be taken as a literal backslash and letter.

When do you use it? When writing to a file with fwrite() or file_put_contents(), sending a text email with mail(), or when adding formatting to pre-populated data in the form element <textarea>. Now, notice I made no mention of HTML output directly. While it’s possible to represent new line, tab, carriage return in HTML if it is within the preformatted tags <pre></pre>, in most cases these tags are not present and HTML will ignore these formatting characters.

Rule #2: Not all computer systems obey the formatting characters the same. When using \n (new line), also include a carriage return (\r) character.

So what do you do if you have a paragraph, for instance submitted by a <textarea> form, that is preformatted and want it to display in the HTML with the \n (new line) breaks represented? That’s when you toss the string into the function nl2br(), which changes all \n to the xhtml line break <br />.

Example:

echo nl2br("Hello\n\rWorld\n\r!!!");

Results:

Hello
World
!!!