grep：最初是 ED 编辑器中的一条命令，用来显示文件中特定的内容，后来成为一个独立的工具 grep。
POSIX（Portable Operating System Interface of Vnix）
The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems.
Perl（Practical Extraction and Reporting Language）
Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier.
Perl Compatible Regular Expressions (PCRE) is a library written in C, which implements a regular expression engine, inspired by the capabilities of the Perl programming language. Philip Hazel started writing PCRE in summer 1997. PCRE's syntax is much more powerful and flexible than either of the POSIX regular expression flavors and than that of many other regular-expression libraries.
A number of prominent open-source programs, such as the Apache and Nginx HTTP servers, and the PHP and R scripting languages, incorporate the PCRE library; proprietary software can do likewise, as the library is BSD-licensed.