Question

As I see in regex documentation that \b match word boundary.
I prepare a string

“db bd how to”

and regex

\b(a|b)(c|d)\b

I think when running the regex, it should match “bd” in the string, but it don’t.

But if the regex is

\\b(a|b)(c|d)\\b

it matches.

Can you explain the difference?

Answer 1

There are several layers of escaping at work here

regex -----------------> | regex literal -> | string literal
-------------------------+------------------+---------------
word boundary            | \b               | \\b
alternation ("a" or "b") | (a|b)            | (a|b)
alternation ("c" or "d") | (c|d)            | (c|d)
word boundary            | \b               | \\b