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→Regular Expression Dialects
* Alternately, use the <code>-E</code> option to make grep understand extended regular expressions, which causes ? + { ( | ) to become special characters.
Other tools, such as sed, similarly require backslashes in front of some of the extended regexp meta-characters(or, if you're using a GNU version of sed, you can use the -E option to enable extended regular expressions, just like GNU grep).
The Perl language introduced one of the most powerful and consistent versions of the regular expression language. There has been increasing consensus around "Perl-Compatible Regular Extensions" (aka PCRE) and that dialect is available in many tools (including GNU grep via the <code>-P</code> option, as well as the [https://www.pcre.org/ PCRE/PCRE2 library] for C and C++ programs, which is used in many software packages including Safari and Apache).
