To determine whether a string contains a complete word, using the preg_match() function with regular expressions is an effective method. 1. Use \b to represent word boundaries to ensure that the matching is a complete word rather than a substring. For example, /\bcat\b/ can avoid matching to category or scat; 2. Add the i flag to implement ignoring case searches, such as /\bapple\b/i can match different formats such as Apple and APPLE; 3. Use | and brackets to implement the "or" relationship search of multiple words, such as /\b(apple|banana|orange)\b/ can be used for keyword filtering or highlighting; 4. Pay attention to common problems: do not miss \b, deal with Chinese spaces and escape special characters, and use preg_quote() to avoid metacharacter interference. Mastering these key points can lead to accurate and safe PHP regular judgment statements.

It is a very practical method to determine whether a string contains a certain word. To put it directly, the key point: using preg_match() function and a suitable regular expression can accurately determine whether the specified complete word exists in the target string.

Distinguish between "contains substrings" and "complete words"

Many newbies will encounter a problem: Why do we use simple strpos() or regular rules like /word/ , but we also include "words"? This is because these methods match substrings, not complete words.

For example:

• Want to find "cat" , but "category" is also matched → Not as expected
• The correct way is to only match "cat" that appears independently

The solution is to use word boundaries ( \b ) to limit the scope:

 if (preg_match('/\bcat\b/i', $text)) {
    // The complete word cat was found
}

This will not miss the hit situation such as category , scat , etc.

Ignore uppercase and uppercase search words

Sometimes we don't care about upper and lower case, such as "Cat", "CAT" and "cat" should all be recognized as the same word. At this time, you can add the i flag to the end of the regular to indicate that upper and lower case is ignored:

 $pattern = '/\bapple\b/i'; // Match Apple, APPLE, aPpLe and aPpLe are fine

This trick is especially useful when handling user input or web content, avoiding missing keywords due to different case.

Multiple words are searched at the same time

If you need to check whether any of the multiple words exists, you can use | to represent the relationship of "or" and use parentheses:

 if (preg_match('/\b(apple|banana|orange)\b/i', $text)) {
    // Match one of the fruits}

This structure is suitable for filtering sensitive words, keyword highlighting and other scenarios.

A few points to note:

• Separate each branch with vertical lines |
• Wrap the whole in brackets to keep the logic clear
• Word boundary \b should be wrapped outside, otherwise the misalignment may be matched

Reminders of common pit points

• Don't forget to add \b : otherwise it will match part of the word, such as searching for "car" may match "scar"
• Be careful of space issues in Chinese environment : There are no spaces to separate words in Chinese, \b may not work the way you expect
• Escape special characters : if there is a word . , * , Wait for regular meta characters, use preg_quote() to process them.

For example:

 $word = preg_quote("test.com", '/');
if (preg_match("/\b{$word}\b/i", $text)) {
    // Safely match test.com
}

Basically that's it. By mastering these key points, you can write accurate and safe PHP regular judgment statements.

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