使用apache ab工具进行测试了下。

ab -n100 -c10 https://you domain/

方法1：原生php函数

$str = 'my_name_is_bill';
echo implode('', array_map(function($val) {
    return ucfirst($val);
}, explode('_', $str)));

测试结果

Concurrency Level:      10
Time taken for tests:   0.657 seconds
Complete requests:      100
Failed requests:        0
Total transferred:      16700 bytes
HTML transferred:       1200 bytes
Requests per second:    152.28 [#/sec] (mean)
Time per request:       65.669 [ms] (mean)
Time per request:       6.567 [ms] (mean, across all concurrent requests)
Transfer rate:          24.83 [Kbytes/sec] received

方法2: 自己编写php代码

$str = 'my';

if ( strpos($str, '_') === false ) {
    echo ucfirst($str);exit;
}

$return = '';
foreach ( explode('_', $str) as $val ) {
    $return .= ucfirst($val);
}

echo $return;

测试结果

Concurrency Level:      10
Time taken for tests:   0.632 seconds
Complete requests:      100
Failed requests:        0
Total transferred:      15700 bytes
HTML transferred:       200 bytes
Requests per second:    158.24 [#/sec] (mean)
Time per request:       63.195 [ms] (mean)
Time per request:       6.320 [ms] (mean, across all concurrent requests)
Transfer rate:          24.26 [Kbytes/sec] received