[Solved] PHP regular expression for given condition [duplicate]

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^(?=.{8,10}$)\d+(?:[ _]\d+)*$

Explanation:

^              # Start of string
 (?=.{8,10}$)  # Assert length 8-10
 \d+           # One or more digits
 (?:           # followed by
  [ _]         #  one space or underscore
  \d+          #  one or more digits
 )*            # zero or more times.           
$              # End of string

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solved PHP regular expression for given condition [duplicate]