PHP Regular Expressions: Pattern Matching, PCRE & Data Validation

A Regular Expression (Regex) is a specialized sequence of characters that forms a search pattern. Whether you need to verify that a user's password contains uppercase letters and digits, extract all URLs from an article, or replace bad words in a forum comment, PCRE (Perl Compatible Regular Expressions) in PHP provide unmatched text-pattern matching power.

Anatomy of a PHP Regular Expression

In PHP, regex patterns are enclosed in forward slashes (delimiters) followed by optional pattern modifiers:

$pattern = "/pattern/modifiers";

• /i Modifier: Case-insensitive matching.
• /m Modifier: Multiline matching.
• /s Modifier: Dot matches all characters including newline.

1. Pattern Matching with preg_match()

<?php
    $str = "Welcome to Veewom Educational Academy";
    $pattern = "/veewom/i"; // Case-insensitive search for "veewom"

    if (preg_match($pattern, $str)) {
        echo "Match found successfully!<br>";
    } else {
        echo "Match not found.<br>";
    }
?>

2. Real-World Validation: Validating Indian Mobile Numbers (10 Digits)

Testing if a mobile number starts with 6-9 and contains exactly 10 digits:

<?php
    $phone = "9876543210";
    // ^ = start, [6-9] = starts with 6,7,8 or 9, [0-9]{9} = 9 more digits, $ = end
    $phoneRegex = "/^[6-9][0-9]{9}$/";

    if (preg_match($phoneRegex, $phone)) {
        echo "Valid 10-digit Indian Mobile Number.<br>";
    } else {
        echo "Invalid Mobile Number format.<br>";
    }
?>

3. Search & Replace with preg_replace()

Replacing words or converting plain text URLs into clickable HTML links:

<?php
    $text = "Visit https://veewom.com for the best PHP 8 tutorials.";

    // Convert raw URLs into clickable anchor tags
    $urlRegex = "/(https?:\/\/[^\s]+)/";
    $linkedText = preg_replace($urlRegex, '<a href="$1" target="_blank">$1</a>', $text);

    echo $linkedText;
?>

BCA / CS University Exam Corner

Interactive Student Practice Session