>perl -wMstrict -le
"my $line = 'Id=\"123\" foo >987<';
 my ($Rkey_id, $Rkey_val) = $line =~ /Id=\"(.*?)\".*?>(.*?)</;
 print $Rkey_id;
 print $Rkey_val;
"
123
987
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Update: see also Set variables from m//.