concatenate value and string

Hi

I try this : is a way to substitute the value "a.owner" with the value of schemas 8in my example ABF17 , ADR07B?

SQL> run
  1* SELECT 'expdp ||a.owner/||a.owner    directory=data_PUMP_DIR  dumpfile=||a.owner.dmp logifile=||a.owner.dmp schemas=' ||a.owner from (select distinct OWNER from dba_segments WHERE TABLESPACE_NAME='ZDBDATA' order by owner asc ) a

expdp ||a.owner/||a.owner  directory=data_PUMP_DIR  dumpfile=||a.owner.dmp logif
ile=||a.owner.dmp schemas=ABF17

expdp ||a.owner/||a.owner  directory=data_PUMP_DIR  dumpfile=||a.owner.dmp logif
ile=||a.owner.dmp schemas=ADR07B