我有一个正则表达式，用于检查长度在4到25个字符之间的用户名，后跟任意可选的空格键和/或单个逗号。您可能已经猜到了，通过键入诸如“ Username1，Username2，Username3”之类的东西，这将用于向几个人发送个人消息。
$rule = "%^\w{4,25}( +)?,?( +)?$%";
preg_match_all($rule, $sendto, $out);
foreach($out[1] as $match) {
echo $match;
}
尽管当我使用preg_match_all（）并尝试对所有值进行排序时，正则表达式似乎正在执行其工作，但它不会向浏览器回显任何内容。我怀疑我对preg_match_all有误解，因为我的正则表达式似乎可以正常工作。
您的正则表达式缺少([\w]{4,25})用户名上的捕获组，请尝试以下操作：
<?
$users = "Username1, Username2 , Username3 ";
preg_match_all('/([\w]{4,25})(?:\s+)?,?/', $users, $result, PREG_PATTERN_ORDER);
foreach($result[1] as $user) {
echo $user;
}
/*
Username1
Username2
Username3
*/
正则表达式说明：
([\w]{4,25})(?:\s+)?,?
Match the regex below and capture its match into backreference number 1 «([\w]{4,25})»
Match a single character that is a “word character” (Unicode; any letter or ideograph, any number, underscore) «[\w]{4,25}»
Between 4 and 25 times, as many times as possible, giving back as needed (greedy) «{4,25}»
Match the regular expression below «(?:\s+)?»
Between zero and one times, as many times as possible, giving back as needed (greedy) «?»
Match a single character that is a “whitespace character” (any Unicode separator, tab, line feed, carriage return, vertical tab, form feed, next line) «\s+»
Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»
Match the character “,” literally «,?»
Between zero and one times, as many times as possible, giving back as needed (greedy) «?»
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