Mid-Atlantic Developer Conference

分隔符

当使用 PCRE 函数的时候,模式需要由分隔符闭合包裹。分隔符可以使任意非字母数字、非反斜线、非空白字符。

经常使用的分隔符是正斜线(/)、hash符号(#) 以及取反符号(~)。下面的例子都是使用合法分隔符的模式。

/foo bar/
#^[^0-9]$#
+php+
%[a-zA-Z0-9_-]%

如果分隔符需要在模式内进行匹配,它必须使用反斜线进行转义。如果分隔符经常在 模式内出现, 一个更好的选择就是是用其他分隔符来提高可读性。

/http:\/\//
#http://#
需要将一个字符串放入模式中使用时,可以用 preg_quote() 函数对其进行 转义,它的第二个参数(可选)可以用于指定需要被转义的分隔符。

除了上面提到的分隔符,也可以使用括号样式的分隔符,左括号和右括号分别作为开始和结束 分隔符。

{this is a pattern}

可以在结束分隔符后面增加模式修饰符。 下面的例子是一个大小写不敏感的匹配:

#[a-z]#i

add a note add a note

User Contributed Notes 5 notes

up
27
Pedro Gimeno
4 years ago
Note that bracket style opening and closing delimiters aren't a 100% problem-free solution, as they need to be escaped when they aren't in matching pairs within the expression. That mismatch can happen when they appear inside character classes [...], as most meta-characters lose their special meaning. Consider these examples:

<?php
  preg_match
('{[{]}', ''); // Warning: preg_match(): No ending matching delimiter '}'
 
preg_match('{[}]}', ''); // Warning: preg_match(): Unknown modifier ']'
 
preg_match('{[}{]}', ''); // Warning: preg_match(): Unknown modifier ']'
?>

Escaping them solves it:

<?php
  preg_match
('{[\{]}', ''); // OK
 
preg_match('{[}]}', ''); // OK
 
preg_match('{[\}\{]}', ''); // OK
?>
up
8
Munin
3 years ago
preg_match('{[}]}', ''); // Warning: preg_match(): Unknown modifier ']'

preg_match('{[\}]}', ''); // OK
up
-4
sln
2 years ago
The dirty little delimiter secret they don't tell you ->
Examples: Balanced delims {\d{2}Some\\{33\\}\w{5}} parses to
\d{2}Some\\{33\\}\w{5} and {\d{2}Some\{33\}\w{5}} parses to \d{2}Some{33}\w{5}. 
Un-Balanced delims +\d{2}Some\+33\+\w{5}+ parses to \d{2}Some+33+\w{5} and
+\d{2}Some\\+33\\+\w{5}+ won't parse because the delimiter is unescaped.
up
-1
Revo
3 months ago
Note that angle brackets `<>` shouldn't be used as delimiters whenever you will have to invoke advanced clusters like atomic groups or lookbehinds because their including angle bracket doesn't come in pair and escaping doesn't help either.
up
-11
hmelin at ya dot ru
2 years ago
A delimiter can be any ASCII non-alphanumeric, non-backslash, non-whitespace character:  !"#$%&'*+,./:;=?@^_`|~-  and  ({[<>]})
To Top