正则表达式在模式涉及美元符号($)时失败 [英] Regex failing when pattern involves dollar sign ($)

问题描述

在匹配涉及美元符号的子模式时，我遇到了一个问题.例如，考虑以下文本块:

I'm running into a bit of an issue when it comes to matching subpatterns that involve the dollar sign. For example, consider the following chunk of text:

Regular Price: $20.50       Final Price: $15.20
Regular Price: $18.99       Final Price: $2.25
Regular Price: $11.22       Final Price: $33.44
Regular Price: $55.66       Final Price: $77.88

我试图用以下正则表达式匹配常规/最终价格集，但根本不起作用(根本没有匹配项):
preg_match_all("/Regular Price: \$(\d+\.\d{2}).*Final Price: \$(\d+\.\d{2})/U", $data, $matches);

I was attempting to match the Regular/Final price sets with the following regex, but it simply wasn't working (no matches at all):
preg_match_all("/Regular Price: \$(\d+\.\d{2}).*Final Price: \$(\d+\.\d{2})/U", $data, $matches);

我逃脱了美元符号，那又能给什么呢?

I escaped the dollar sign, so what gives?

推荐答案

在双引号字符串内，反斜杠被视为$的转义字符.即使在preg_match_all函数看到反斜杠之前，PHP解析器也会删除反斜杠:

Inside a double quoted string the backslash is treated as an escape character for the $. The backslash is removed by the PHP parser even before the preg_match_all function sees it:

$r = "/Regular Price: \$(\d+\.\d{2}).*Final Price: \$(\d+\.\d{2})/U";
var_dump($r);

输出( ideone ):

"/Regular Price: $(\d+\.\d{2}).*Final Price: $(\d+\.\d{2})/U"
                 ^                           ^
              the backslashes are no longer there

要解决此问题，请使用单引号字符串而不是双引号字符串:

To fix this use a single quoted string instead of a double quoted string:

preg_match_all('/Regular Price: \$(\d+\.\d{2}).*Final Price: \$(\d+\.\d{2})/U',
               $data,
               $matches);

查看其在线运行情况: ideone

See it working online: ideone

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