本文介绍了在POSIX扩展正则表达式中使用的14种元字符，这些元字符在正则表达式中有特殊含义，当需要将其作为普通字符使用时，必须用反斜杠进行转义。
A metacharacter is a character that has a special meaning (instead of a literal meaning) to a computer program, such as a shell interpreter or a regular expression engine.
In POSIX extended regular expressions,[1] there are 14 metacharacters that must be preceded by a backslash “\” in order to drop their special meaning and be treated literally inside an expression: the open/close square brackets, “[” and “]”; the backslash “\”; the caret “^”; the dollar sign “$”; the period or dot “.”; the vertical bar or pipe symbol “|”; the question mark “?”; the asterisk “*”; the plus-sign “+”; open/close curly braces, “{” and “}”; and open/close parenthesis, “(” and “)“.
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