正则表达式可选匹配行开始/结束

How do I optionally match the start ^ or end $ of a line in a regular expression.

我如何选择匹配行的开始^或者结束美元在一个正则表达式。

For example:

例如:

/(?<=[\s\^])/ does not match starts with space character or start of line.

/(? < =[\ s \ ^])/不匹配开头空格字符或线的开始。

As requested my problem was in PHP matching the following.

根据请求，我的问题是在PHP中匹配以下内容。

$str = '**bold** **bold** **bold**';
echo preg_replace('/(?<=\s|^)\*\*(.+?)\*\*(?=\s|$)/', '<strong>\\1</strong>', $str);

My edge cases were the bold at the start and end of the string were not being matched. Some edge cases I came across with other variants were matching within strings, matching chains of asterisks, and countless other problems.

我的边缘是粗体在开始和结束的弦没有被匹配。我遇到过的一些边的例子有字符串内的匹配，星号链的匹配，还有无数其他的问题。

echo preg_replace('/(?<=^|\s|\>)[\*]{2,}(?=[^\s\*])(.+?)(?<=[^\s\*])[\*]{2,}(?=\s|\<|$)/', '<strong>\\1</strong>', $str);

3 个解决方案

#1

If you insist on matching after a whitespace character or the start of the line use an alternation (not the character class). Assuming your regex flavour supports alternations in lookbehind assertions.

如果您坚持在空格字符或行开始之后进行匹配，请使用替换(而不是字符类)。假设您的regex风味支持在查找断言后进行更改。

/(?<=\s|^)\w+/m

but probably you are looking for a word boundary \b? They match on the start or end of a word. (Exactly on the change from a word character to a non word character or the other way round)

但是你可能在找一个单词boundary \b?它们在单词的开头或结尾进行匹配。(从一个字字符到一个非字字符或者反过来)

You should give us more information: the language, the input and the expected result (including corner cases).

您应该向我们提供更多的信息:语言、输入和预期结果(包括角落情况)。

#2

Just remove the anchors. Without the anchors, the regex will be matched anywhere in the string you are searching.

只是删除锚点。没有锚，regex将被匹配到您正在搜索的字符串中的任何位置。

#3

Look at this:

看看这个:

http://www.w3schools.com/jsref/jsref_obj_regexp.asp

http://www.regular-expressions.info/anchors.html

Regular expression - starting and ending with a letter, accepting only letters, numbers and _

正则表达式——以字母开头和结尾，只接受字母、数字和_

cheers!

干杯!

#1