What is word boundary in regular expression?

In regular expressions, a word boundary is a zero-width assertion, meaning it doesn't match any characters, but it asserts a specific condition about the surrounding characters. It matches the position between a word character (alphanumeric or underscore) and a non-word character, or at the beginning or end of the string.

Here's a breakdown:

What it matches:

* Between word and non-word characters:

* `\bcat\b` matches "cat" but not "caterpillar" or "tomcat".

* Beginning of string:

* `\bcat` matches "cat" in "catapult" but not in "tomcat".

* End of string:

* `cat\b` matches "cat" in "catapult" but not in "tomcat".

What it doesn't match:

* Inside a word:

* `\bcat\b` will not match "cat" in "tomcat" because it's inside a word.

* Between two non-word characters:

* `\bcat\b` will not match "cat" in "123cat456" because it's between two non-word characters.

Common uses:

* Precise word matching: You can use it to ensure you only match a complete word and not parts of words within larger text.

* Finding words at specific positions: For example, you can find words at the beginning or end of a line or string.

* Excluding unwanted matches: You can use word boundaries to avoid matching parts of words that you don't want.

Example:

```regex

\bcat\b

```

This regular expression will match the word "cat" when it appears as a complete word. It will not match "cat" in "tomcat" or "caterpillar."

Note:

* The word boundary assertion is represented by `\b`.

* The word characters are typically defined as `[A-Za-z0-9_]`, but this may vary depending on the specific regex engine.

* In some programming languages, the syntax might be different.

Understanding word boundaries is crucial for crafting precise and efficient regular expressions that accurately capture the desired matches in your text.