Regular Expression Tips & Tutorials

PHP preg_match() First Letter of a WordPress Post for Drop Cap Styling

While CSS3 can target the first letter of text inside an element, it’s still not universally supported across major browsers AND it doesn’t work well for elements that have child elements inside. The bullet proof way to target the first letter of a WordPress post would be to capture the content of the post in …

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A small mistake in a regular expression caused connection to reset – (.+)+

Was doing something with a regular expression and very oddly the connection keeps being reset every time I refresh the web page. I tried to narrow down the problematic line by removing the code in functional chunks. Finally it comes down to a preg_match() instance with a small bit in the regular expression that’s accidentally …

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Regular Expression for Date and Time Strings

Often we need the users to enter a valid string of date or time in the form. But how do you validate the strings with regular expressions? In PHP, you can use these functions and regular expressions. RegExp and function to validate against date string: // Default: YYYY-MM-DD function isDate($subject, $separator = ‘-‘) { return …

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Regular Expressions for Natural Numbers or Positive Integers (1, 2, 3, …), Negative Integers and Non-negative Integers

When I’m developing the online form creator that enables the users to create form fields that accept only certain type of numbers, I need to verify if a given string is a valid natural number such as 1, 2, 3, 4, …. I’m writing the code / functions in PHP but you can literally use …

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PHP: Check or Validate URL and Email Addresses – an Easier Way than Regular Expressions, the filter_var() Function

To check if a URL or an email address is valid, the common solution is regular expressions. For instance, to validate an email address in PHP, I would use: if (preg_match(‘|^[A-Z0-9._%+-][email protected][A-Z0-9.-]+\.[A-Z]{2,4}$|i’, $email)) { // $email is valid } A simpler and more forgiving one would be: |^\[email protected]\S+\.\S+$| Which is usually quite enough for signup forms …

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PHP: Subject String Length Limit of Regular Expression Matching Functions

Here’s a quick tip for those who have encountered this very same problem that all regular expression functions of PHP such as preg_match() and preg_replace() stop working when the input string (subject string to be searched or matched) is too long or large. If you believe your regular expressions should work but didn’t and the …

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PHP: Generating Summary Abstract from A Text or HTML String, Limiting by Words or Sentences

On index or transitional pages, such as homepage or category pages of WordPress, you don’t want to show the full texts of your deep content pages yet but just a content snippet of the first few sentences or words as a summary with a read more link to the actual article. This is generally good …

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