不幸的是，(和\(之类的东西的含义在Emacs样式的正则表达式和大多数其他样式之间交换。因此，如果你试图逃避这些，你可能会做与你想要的相反的事情。

所以你必须知道你想引用的是什么风格。

现代正则表达式口味(PCRE)

包括C、c++、Delphi、EditPad、Java、JavaScript、Perl、PHP (preg)、PostgreSQL、PowerGREP、PowerShell、Python、REALbasic、Real Studio、Ruby、TCL、VB。Net, VBScript, wxWidgets, XML Schema, Xojo, XRegExp。PCRE兼容性可能有所不同

不会后悔:。^ $ * + - ?( ) [ ] { } \ |

传统RegEx口味(BRE/ERE)

包括awk, ed, egrep, emacs, GNUlib, grep, PHP (ereg)， MySQL, Oracle, R, sed。PCRE支持可以在后续版本中启用或通过使用扩展启用

纪念awk / egrep / emacs

在字符类之外:。^ $ * + ?() [{} \ | . 在字符类中:^ - []

BRE / ed / grep和sed

在字符类之外:。^ $ * [\ 在字符类中:^ - [] 对于字面量，不要转义:+ ?() {} | 对于标准的正则表达式行为，转义:\+ \?\(\) \{\} \|

笔记

If unsure about a specific character, it can be escaped like \xFF Alphanumeric characters cannot be escaped with a backslash Arbitrary symbols can be escaped with a backslash in PCRE, but not BRE/ERE (they must only be escaped when required). For PCRE ] - only need escaping within a character class, but I kept them in a single list for simplicity Quoted expression strings must also have the surrounding quote characters escaped, and often with backslashes doubled-up (like "(\")(/)(\\.)" versus /(")(\/)(\.)/ in JavaScript) Aside from escapes, different regex implementations may support different modifiers, character classes, anchors, quantifiers, and other features. For more details, check out regular-expressions.info, or use regex101.com to test your expressions live

真的，没有。正则表达式语法大约有无数种;它们似乎可以归结为Perl、EMACS/GNU和AT&T，但我也总是感到惊讶。

为了避免担心哪个regex变量和所有定制的特性，只需使用这个通用函数，它涵盖了除了BRE之外的每个regex变量(除非它们有unicode多字节字符是元字符):

jot -s '' -c - 32 126 | 

mawk ' 功能 重返substr(_ =””, gsub ("[][!-/_\ 140 :-@{-~]","[&]",__), gsub ("["(_="\\\\")"^]",_ "&",__))__ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

 !"#$%&'()*+,-./0123456789:;<=>?
@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_
`abcdefghijklmnopqrstuvwxyz{|}~

    [!]["][#][$][%][&]['][(][)][*][+][,][-][.][/]
  0  1  2  3  4  5  6  7  8  9 [:][;][<][=][>][?]
 [@] ABCDEFGHIJKLMNOPQRSTUVWXYZ   [[]\\ []]\^ [_]
 [`] abcdefghijklmnopqrstuvwxyz   [{][|][}][~]

方括号更容易处理，因为没有触发关于“转义太多”的警告信息的风险，例如:

function ____(_) {
    return substr("", gsub("[[:punct:]]","\\\\&",_))_ 
} 

                     \!\"\#\$\%\&\'\(\)\*\+\,\-\.\/ 0123456789\:\;\<\=\>\?
\@ABCDEFGHIJKLMNOPQRSTUVWXYZ\[\\\]\^\_\`abcdefghijklmnopqrstuvwxyz \{\|\}\~

gawk: cmd. line:1: warning: regexp escape sequence `\!' is not a known regexp operator
gawk: cmd. line:1: warning: regexp escape sequence `\"' is not a known regexp operator
gawk: cmd. line:1: warning: regexp escape sequence `\#' is not a known regexp operator
gawk: cmd. line:1: warning: regexp escape sequence `\%' is not a known regexp operator
gawk: cmd. line:1: warning: regexp escape sequence `\&' is not a known regexp operator
gawk: cmd. line:1: warning: regexp escape sequence `\,' is not a known regexp operator
gawk: cmd. line:1: warning: regexp escape sequence `\:' is not a known regexp operator
gawk: cmd. line:1: warning: regexp escape sequence `\;' is not a known regexp operator
gawk: cmd. line:1: warning: regexp escape sequence `\=' is not a known regexp operator
gawk: cmd. line:1: warning: regexp escape sequence `\@' is not a known regexp operator
gawk: cmd. line:1: warning: regexp escape sequence `\_' is not a known regexp operator
gawk: cmd. line:1: warning: regexp escape sequence `\~' is not a known regexp operator

https://perldoc.perl.org/perlre.html#Quoting-metacharacters和https://perldoc.perl.org/functions/quotemeta.html

在官方文档中，这样的字符称为元字符。引用的例子:

my $regex = quotemeta($string)
s/$regex/something/

POSIX识别正则表达式的多种变体——基本正则表达式(BRE)和扩展正则表达式(ERE)。即使这样，由于POSIX标准化的实用程序的历史实现，也存在一些怪癖。

对于何时使用哪种符号，甚至给定命令使用哪种符号，并没有一个简单的规则。

看看Jeff Friedl的《精通正则表达式》这本书。