Test your regular expression knowledge. how can this problem be solved?

Test your regular expression knowledge 192.168.93.24 '2017-03-2012: 02: 05 'Get/91063b13bf8ba59b896804d829b0ff20/3110/apk/index. php? System = source & amp; modu test your regular expression knowledge
192.168.93.24 '2017-03-31 10:02:05 'GET/91063b13bf8ba59b896804d829b0ff20/2012/apk/index. php? System = source & module = bibei & app = 0 & f = 9_3_0_0_0 'http: // 192.168.93.55: 9090/apk/index. php? App = 0'mozilla/5.0 (Windows NT 5.1) AppleWebKit/535.7 (KHTML, like Gecko) Chrome/16.0.912.0 Safari/535.7

There is such a string, note that there is such a string f = 9_3_0_0_0, it may or may not exist, its location is not fixed, just know that it must be behind hello, 'front, to do this, try to match the five digits after f = (not fixed). if there is no f parameter, you can obtain all the values blank. Thank you!

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So?
Preg_match_all ('/\ bf = ([\ d _] +) \ B/M', $ s, $ r );
Print_r ($ r [1]);

Array
(
[0] => 9_3_0_0_0
)

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I have been reading this question for a long time.

PHP code

$ Str = <
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192.168.93.24 '2017-03-31 10:02:05 'GET/91063b13bf8ba59b896804d829b0ff20/2012/apk/index. php? System = albums & module = list & app = 0 'http: // 192.168.93.55: 9090/apk/index. php? Syste
   
M = source &......