$text =~ 
  s{         # Substitute
     \A      #   from the beginning of the string
     \s+     #   one or more white space characters
   }{}xms;  # with nothing

$text =~ 
  s{         # Substitute
     \s+     #   one or more white space characters
     \z      #   from the end of the string
   }{}xms;   # with nothing

$text =~ 
  s{         # Substitute
     \s+     #   one or more white space characters
   }{ }gxms; # with one space, anywhere in the string
             # As many times as it occurs