捕获组VS非捕获组

I tried to test the performance of capturing and non-capturing group of the regex. By the way, there is very slightly different between the capturing group and the non-capturing group. Is this result normal?

我试图测试正则表达式的捕获和非捕获组的性能。顺便说一下，捕获组和非捕获组之间存在非常小的差异。这个结果是否正常？

[root@Sensor ~]# ll -h sample.log
-rw-r--r-- 1 root root 21M Oct 20 23:01 sample.log

[root@Sensor ~]# time grep -ciP '(get|post).*' sample.log
20000

real    0m0.083s
user    0m0.070s
sys     0m0.010s

[root@Sensor ~]# time grep -ciP '(?:get|post).*' sample.log
20000

real    0m0.083s
user    0m0.077s
sys     0m0.004s

2 个解决方案

#1

Typically, non-capturing groups perform better than capturing groups, because they require less allocation of memory, and do not make a copy of the group match. However, there are three important caveats:

通常，非捕获组的性能优于捕获组，因为它们需要较少的内存分配，并且不会复制组匹配。但是，有三个重要的警告：

The difference is typically very small for simple, short expressions with short matches.
对于具有短匹配的简单短表达，差异通常非常小。
The act of starting a program like grep itself takes a significant amount of time and memory, and may overwhelm any small improvement gained by using non-capturing group(s).
启动像grep这样的程序的行为需要大量的时间和内存，并且可能会超过使用非捕获组所获得的任何小改进。
Some languages implement capturing and non-capturing groups in the same way, causing the latter to give no performance improvement.
有些语言以相同的方式实现捕获和非捕获组，导致后者不会提高性能。

#2

If use a lot of the capturing group. The difference seems to be more.

如果使用了很多捕获组。差异似乎更多。

Thanks everyone.:)

感谢大家。：）

[root@Sensor ~]# time grep -ciP "(get|post)\s[^\s]+" sample.log
20000

real    0m0.057s
user    0m0.051s
sys     0m0.005s
[root@Sensor ~]# time grep -ciP "(?:get|post)\s[^\s]+" sample.log
20000

real    0m0.061s
user    0m0.053s
sys     0m0.006s
[root@Sensor ~]# time grep -ciP "(get|post)\s[^\s]+(get|post)" sample.log
1880

real    0m0.839s
user    0m0.833s
sys     0m0.005s
[root@Sensor ~]# time grep -ciP "(?:get|post)\s[^\s]+(?:get|post)" sample.log
1880

real    0m0.744s
user    0m0.741s
sys     0m0.003s

#1