c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = qq{0 (0) tracegen chn:req cmd:SDP_CMD_RDSIZED unit:0x10 addr:0x0 len:0x3f vc:0 qospri:0 qosfw:0 strm:0x0 chain:0 io:0\n};
 ;;
 my $address = '500000000';
 ;;
 $s =~ s{ (?<= addr:0x) [[:xdigit:]]+ }{$address}xms;
 ;;
 my $expected = qq{0 (0) tracegen chn:req cmd:SDP_CMD_RDSIZED unit:0x10 addr:0x500000000 len:0x3f vc:0 qospri:0 qosfw:0 strm:0x0 chain:0 io:0\n};
 print 's/// ok' if $s eq $expected;
"
s/// ok