$ perl -Mstrict -Mwarnings -E '
my $regex = do {
   my @range1 = 1 .. 8;
   my @range2 = 1 .. 48;
   local $" = q{|};
   qr{(?x) ^ GigabitEthernet ( @range1 ) / 0 / ( @range2 ) $ };
   };
say $regex;

say
   qq{$_: },
   m{$regex}
   ? q{MATCHED}
   : q{FAILED}
   for qw{
      GigabitEthernet1/0/48
      GigabitEthernet1/0/49
      GigabitEthernet1/0/236
      GigabitEthernet31/0/48
      GigabitEthernet3/0/13
      };'
(?^u:(?x) ^ GigabitEthernet ( 1|2|3|4|5|6|7|8 ) / 0 / ( 1|2|3|4|5|6|7|8|9|10|11|12|13|14|15|16|17|18|19|20|21|22|23|24|25|26|27|28|29|30|31|32|33|34|35|36|37|38|39|40|41|42|43|44|45|46|47|48 ) $ )
GigabitEthernet1/0/48: MATCHED
GigabitEthernet1/0/49: FAILED
GigabitEthernet1/0/236: FAILED
GigabitEthernet31/0/48: FAILED
GigabitEthernet3/0/13: MATCHED
$