Metacharacter

The article's lead section may need to be rewritten. The reason given is: definition and lead are only about regular expression metacharacters, but article is not. Please help improve the lead and read the lead layout guide. (April 2019) (Learn how and when to remove this message)

A metacharacter is a character that has a special meaning to a computer program, such as a shell interpreter or a regular expression (regex) engine.

In POSIX extended regular expressions, there are 14 metacharacters that must be escaped (preceded by a backslash (\)) in order to drop their special meaning and be treated literally inside an expression: opening and closing square brackets ([ and ]); backslash (\); caret (^); dollar sign ($); period/full stop/dot (.); vertical bar/pipe symbol (|); question mark (?); asterisk (*); plus and minus signs (+ and -); opening and closing curly brackets/braces ({ and }); and opening and closing parentheses (( and )).

For example, to match the arithmetic expression (1+1)*3=6 with a regex, the correct regex is \(1\+1\)\*3=6; otherwise, the parentheses, plus sign, and asterisk will have special meanings.