Find the name of an oracle instance,or if the instance is up

$ ps -ef | grep ora_smon
oracle 8711 8669 0 16:15 pts/1 00:00:00 grep ora_smon
$ cat /etc/oratab
....
orcl:/home/oracle/10.1:Y
...
$cd $ORACLE_HOME/dbs
$ls -l spfile*