我会使用正则表达式和自定义回调，如下所示:

I would use a regex and a custom callback, like this:

$str = "Line <br> Line <br> Line <br> Line <br>";
$replace = array("1", "2", "3", "4");
$str = preg_replace_callback( '/<br>/', function( $match) use( &$replace) {
    return array_shift( $replace) . ' ' . "
";
}, $str);

请注意，这里假设我们可以修改 $replace 数组.如果不是这种情况，您可以保留一个计数器:

Note that this assumes we can modify the $replace array. If that's not the case, you can keep a counter:

$str = "Line <br> Line <br> Line <br> Line <br>";
$replace = array("1", "2", "3", "4");
$count = 0;
$str = preg_replace_callback( '/<br>/', function( $match) use( $replace, &$count) {
    return $replace[$count++] . ' ' . "
";
}, $str);

你可以从这个演示看到它输出:

Line 1 Line 2 Line 3 Line 4