Why was \b introduced while \s match string borders in regular expressions?

Question

I see that there is the \b which I have never used and I was wondering if someone can give me use cases when it is not possible to do without \b.

Answer 1

I was wondering if someone can give me use cases when it is not possible to do without \b.

The expression \b is just a convenient shorthand for what you can already do with other constructs.

For example, if your regular expression engine has lookarounds then \b is equivalent to the following longer expression:

(?<=\w)(?!\w)|(?<!\w)(?=\w)

Similarly \w, \d, etc. are just shorthand for what already can be done using character classes, for example [A-Za-z0-9_] or [0-9]. You typically want to use the short version because writing out the full definition each time is cumbersome, harder to read and increases the risk of making an error.

Answer 2

They match on different things - \s matches on whitespace, \b on word boundaries.

One good example is the character ..

In the string hello.hi:

\s will not match ., but \b will match before and after it.