PHP Preg替换多个下划线

如何使用preg_replace将多个下划线替换为一个下划线？

preg_replace（“/[\u]+/”、“\u”、$your_string）

操作符匹配最后一个字符（或捕获组）的多个实例

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我不知道您想使用preg_replace的原因，但有什么问题：

str_replace('__', '_', $string);

需要+运算符

$text = "______";
$text = preg_replace('/[_]+/','_',$text);

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运行测试时，我发现：

while (strpos($str, '__') !== false) {
    $str = str_replace('__', '_', $str);
}

要始终比这更快：

$str = preg_replace('/[_]+/', '_', $str);

我使用以下方法生成了不同长度的测试字符串：

$chars = array_merge(array_fill(0, 50, '_'), range('a', 'z'));
$str = '';
for ($i = 0; $i < $len; $i++) {  // $len varied from 10 to 1000000
    $str .= $chars[array_rand($chars)];
}
file_put_contents('test_str.txt', $str);

以及：

对于较短的字符串，str_replace（）方法比preg_replace（）方法快25%。字符串越长，差异越小，但是str_replace（）总是更快

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我知道有些人出于速度以外的原因更喜欢一种方法，我很乐意阅读有关结果、测试方法等的评论。

实际上使用

/\uu+/

或

/{2，}/

比

/\u+/

更好，因为不需要替换一个下划线。这将提高preg变量的速度。

这将只接受将替换为的字符、数值或特殊字符_
This will Accept Only Characters,numeric value or Special Character found it will replace with _
<?php
error_reporting(0);
if($_REQUEST)
{
    PRINT_R("<PRE>");
    PRINT_R($_REQUEST);
    $str=$_REQUEST[str];
    $str=preg_replace('/[^A-Za-z\-]/', '_', $str);
    echo strtolower(preg_replace('/_{2,}/','_',$str));
}
?>
<form action="" method="post">
<input type="text" name="str"/>
<input type="submit" value="submit"/>
</form>

您还可以使用具有自动分隔符的

pattern('_+')->replace($your_string)->with('_');

---

因为它不会将

\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu->
（1）等等，不需要定义字符类。这是真的，但我还是这么做了。看来我并不孤单。
$str = file_get_contents('test_str.txt');
$start = microtime(true);
while (strpos($str, '__') !== false) {
    $str = str_replace('__', '_', $str);
}
echo microtime(true) - $start;

This will Accept Only Characters,numeric value or Special Character found it will replace with _
<?php
error_reporting(0);
if($_REQUEST)
{
    PRINT_R("<PRE>");
    PRINT_R($_REQUEST);
    $str=$_REQUEST[str];
    $str=preg_replace('/[^A-Za-z\-]/', '_', $str);
    echo strtolower(preg_replace('/_{2,}/','_',$str));
}
?>
<form action="" method="post">
<input type="text" name="str"/>
<input type="submit" value="submit"/>
</form>

pattern('_+')->replace($your_string)->with('_');