基本上我在$textvar 中存储了以下文本：
$text = 'An airplane accelerates down a runway at 3.20 m/s2 for 32.8 s until is finally lifts off the ground. Determine the distance traveled before takeoff'.
我有一个函数，它从名为 which 的数组中替换文本上的一些关键字$replacements（我在上面做了一个 var_dump）：
'm' => string 'meter' (length=5)
'meters' => string 'meter' (length=5)
's' => string 'second' (length=6)
'seconds' => string 'second' (length=6)
'n' => string 'newton' (length=6)
'newtons' => string 'newton' (length=6)
'v' => string 'volt' (length=4)
'speed' => string 'velocity' (length=8)
'\/' => string 'per' (length=3)
's2' => string 'secondsquare' (length=12)
文本通过以下功能：
$toreplace = array_keys($replacements);
foreach ($toreplace as $r){
$text = preg_replace("/\b$r\b/u", $replacements[$r], $text);
}
但是，我的期望与输出之间存在差异：
Expected Output : an airplane accelerates down runway at 3.20 meterpersecondsquare for 32.8 second until finally lifts off ground determine distance traveled before takeoff
Function Output : an airplane accelerates down runway at 3.20 meterpers2 for 32.8 second until finally lifts off ground determine distance traveled before takeoff
请注意，我期望 'meterpersecondsquare' 并且得到 'meterpers2'（'s2' 没有被替换），而 'm' 和 '/' 被替换为它们的值。
我注意到当我使用 m/s 而不是 m/s2 时，它可以正常工作并给出：
an airplane accelerates down runway at 3.20 meterpersecond for 32.8 second until finally lifts off ground determine distance traveled before takeoff
所以问题基本上是它与s2不匹配。任何想法为什么会这样？