5.2 Backslash Character

The `\' when followed by certain ordinary characters take a special meaning :

``\b''

Match the empty string at the edge of a word.

``\B''

Match the empty string provided it's not at the edge of a word.

``\<''

Match the empty string at the beginning of word.

``\>''

Match the empty string at the end of word.

``\w''

Match word constituent, it is a synonym for `[[:alnum:]]'.

``\W''

Match non word constituent, it is a synonym for `[^[:alnum:]]'.

For example , `\brat\b' matches the separate word `rat', `c\Brat\Be' matches `crate', but `dirty \Brat' doesn't match `dirty rat'.