正则表达式用于转义尚未转义的单引号

Question

我想将'替换为\'，而不是\'，因为它们已被转义。

Answer 1

使用 lookarounds 非常简单：

(?<!\\)'

请参阅a demo on regex101.com 您还需要为PHP：

转义反斜杠

<?php
$string = "I want to replace ' with \' but not \' since they are already escaped";
$regex = "~(?<!\\\)'~";

echo preg_replace($regex, "\\'", $string);
# Output: I want to replace \' with \' but not \' since they are already escaped

?>

参见 a demo on ideone.com 。