ps-ef|grep pmon (Instance Name Only)
$ ps -ef | grep pmon | grep -v grep
oracle   23955     1  0 Jan16 ?        00:00:33 asm_pmon_+ASM
oracle   27366     1  0 Jan16 ?        00:00:31 ora_pmon_S112

$ ps -ef | grep pmon | grep -v grep | awk '{ print $8 }' | cut -d '_' -f3
+ASM
S112

$ ps -e -o command | grep pmon | grep -v grep | cut -d '_' -f3
+ASM
S112