In a mongod started up with the following argv, I would expect the parsed field to contain replication.replSetName not replication.replSet.
I realize that it is debatable whether or not the current behavior is wrong. However, I would expect the output of parsed to match the YAML-style in all cases, not be a mixture of YAML-style and legacy-style.
backup_test:PRIMARY> db.runCommand('getCmdLineOpts') { "argv" : [ "mongod", "--port=27000", "--replSet=backup_test", "--dbpath=/Users/cailin/Documents/code/mms/data/db/replica/backup_test/backup_test_0", "--logpath=/Users/cailin/Documents/code/mms/data/db/replica/backup_test/backup_test_0/mongodb.log", "--logappend", "--nojournal" ], "parsed" : { "net" : { "port" : 27000 }, "replication" : { "replSet" : "backup_test" }, "storage" : { "dbPath" : "/Users/cailin/Documents/code/mms/data/db/replica/backup_test/backup_test_0", "journal" : { "enabled" : false } }, "systemLog" : { "destination" : "file", "logAppend" : true, "path" : "/Users/cailin/Documents/code/mms/data/db/replica/backup_test/backup_test_0/mongodb.log" } }, "ok" : 1 }