Regular expressions are used to match text. The term is used to describe the loosely defined text-matching language as well as the patterns themselves. A regular expression is often called a regex or a regexp.
Regular expressions are made up of metacharacters (with special meaning) and literals (everything that is not a metacharacter).
The backslash character (
\) turns off (escapes) the special meaning of the character that follows, turning metacharacters into literals. For nonmetacharacters, it often turns on some special meaning.