Syntax
A number of special characters or meta characters are used to denote actions or delimit groups; but it is possible to force these special characters to be interpreted as normal characters by preceding them with a defined escape character, usually the backslash "\". For example, a dot is normally used as a "wild card" metacharacter to denote any character, but if preceded by a backslash it represents the dot character itself. The pattern c.t matches "cat", "cot", "cut", and non-words such as "czt" and "c.t"; but c\.t matches only "c.t". The backslash also escapes itself, i.e., two backslashes are interpreted as a literal backslash character.
Read more about this topic: Regular Expression