当haystack是exec()输出时，Preg_match返回null - preg_match returns null when the haystack is an exec() output

preg_match returns null when the haystack is an exec() output

我试图在使用exec()运行的Linux命令的输出上运行一些正则表达式。当插入exec()输出作为干草堆时，preg_match返回NULL，但是当我将此输出的相同副本放入字符串并将其用作干草堆时，preg_match工作良好并输出预期的数组。

代码:

exec("/usr/local/bin/ffmpeg -i video.flv 2>&1 | grep Duration", $output);
//$output[0] will be: "Duration: 00:01:00.08, start: 0.042000, bitrate: 164 kb/s"    
$string = $output[0];    
//This regex is to extract the duration, "00:01:00", from the output.
$pattern = "/(^Duration:) ([^&]+)(.[0-9][0-9])(, start)/";    
preg_match($pattern, $string, $matches);
print_r($matches[2]);
//The result should be "00:01:00" but the whole $matches array is empty instead.
//If I added the result of output[0] manually into a string it works fine.
$str = "Duration: 00:01:00.08, start: 0.042000, bitrate: 164 kb/s";
preg_match($pattern, $str, $matches_);
print_r($matches_[2]);
//Outputs "00:01:00" and everything is working fine.
//Just to make sure, I printed $str and $string to see if there is any difference
echo $str."'n".$string;
//The output is:
//Duration: 00:01:00.08, start: 0.042000, bitrate: 164 kb/s
//Duration: 00:01:00.08, start: 0.042000, bitrate: 164 kb/s

使用以下echo命令，使用单引号分隔字符串:

echo "'$str''n'$string'";

输出:

'Duration: 00:01:00.08, start: 0.042000, bitrate: 164 kb/s'
'  Duration: 00:01:12.66, start: 0.000000, bitrate: 127 kb/s'

你看，它们不一样。Ffmpeg在字符串前面添加空白。

但是，如果您将模式更改为:

则没有关系。

$pattern = "/(Duration:) ([^&]+)(.[0-9][0-9])(, start)/";

注意，我把^放在Duration前面。现在模式匹配了，尽管字符串前面有一些空白。