Preg_replace ('/^. +? /U', '', $ auth) to solve this regular expression?

What does this php function mean? Preg_replace (& #039; ^. +? U & #039;, & #039; & #039;, $ auth) What does this php function mean?
Preg_replace ('/^. +? /U', '', $ auth)

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What does this php function mean?
Preg_replace ('/^. +? /U', '', $ auth)

FunctionPreg_replaceYou should know how to use regular expressions to replace strings. If you do not understand the regular expression, read the official documentation.

Let me explain this regular expression.'/^. +? /U'.

ModifierUIndicates reversing the greedy mode 」.
Regular Expressions are greedy by default, that is+ *If multiple characters can be matched, try to match more characters unless+? *?.
HoweverUAfter modifier, the greedy mode is not used by default,+ *Non-Greedy match,+? *?Instead, try to match more characters.
For more details, see the official documentation or searchRegular Expression PCRE_UNGREEDY.

So,/^. +? /UActually equivalent/^. +/, Indicates all characters starting from the beginning.

Therefore, this function means to replace all the characters starting from the beginning with an empty string. (Although I don't know what it means to write such a round expression in addition to the interview test)