There's no reason to do this with one expression.

my ($tot, $gcount, $ccount, $ocount);
while (<>) {
  $tot=$1 if /^Total count\s+(\d+)/;
  $gcount = $1 if /^G\s+(\d+)/;
  $ccount = $1 if /^C\s+(\d+)/;
  $ocount = $1 if /^Other\s(\d+)/;
}
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You could do a series of if..elsif..elsifs, if you preferred.