如何在不解释元字符的情况下将变量用于正则表达式模式? [英] How can I use a variable for a regex pattern without interpreting meta characters?

问题描述

$text_to_search = "example text with [foo] and more";
$search_string = "[foo]";

if ($text_to_search =~ m/$search_string/)
    print "wee";

请注意上面的代码.出于某种原因，我想在 $text_to_search 变量中找到文本[foo]"，如果找到就打印wee".为此，我必须确保将 [ 和 ] 替换为 [ 和 ] 以使 Perl 将其视为字符而不是运算符.

Please observe the above code. For some reason I would like to find the text "[foo]" in the $text_to_search variable and print "wee" if I find it. To do this I would have to ensure that the [ and ] is substituted with [ and ] to make Perl treat it as characters instead of operators.

如何在不必先将 [ 和 ] 替换为 \[ 和 \] 的情况下执行此操作使用 s/// 表达式?

How can I do this without having to first replace [ and ] with \[ and \] using a s/// expression?

推荐答案

使用 \Q 自动转义变量中任何可能有问题的字符.

Use \Q to autoescape any potentially problematic characters in your variable.

if($text_to_search =~ m/\Q$search_string/) print "wee";

更新:为了阐明这是如何工作的...

Update: To clarify how this works...

\Q 将打开自动转义"；正则表达式中的特殊字符.这意味着任何在匹配运算符中具有特殊含义的字符(例如，*、^ 或 [ 和 ]) 将在它们之前插入一个 \ 以关闭它们的特殊含义.

The \Q will turn on "autoescaping" of special characters in the regex. That means that any characters which would otherwise have a special meaning inside the match operator (for example, *, ^ or [ and ]) will have a \ inserted before them so their special meaning is switched off.

自动转义一直有效，直到发生两种情况之一.在字符串中找到 \E 或到达字符串末尾.

The autoescaping is in effect until one of two situations occurs. Either a \E is found in the string or the end of the string is reached.

在我上面的例子中，没有必要关闭自动转义，所以我省略了 \E.如果稍后需要在正则表达式中使用正则表达式元字符，则需要使用 \E.

In my example above, there was no need to turn off the autoescaping, so I omitted the \E. If you need to use regex metacharacters later in the regex, then you'll need to use \E.

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