If we try to export a dumpfile with the name, which is already present in that directory. then we will get error like ORA-27038: created file already exists

ORA-39001: invalid argument value
ORA-39000: bad dump file specification
ORA-31641: unable to create dump file “/export/home/oracle/dbaclass_estim.dmp“
ORA-27038: created file already exists
Additional information: 1

So if the requirement is to overwrite the existing dumpfile, then REUSE_DUMPFILES parameter can be used with EXPDP.

REUSE_DUMPFILES
Overwrite destination dump file if it exists [NO].

DEMO:

PARFILE WITH REUSE_DUMPFILES=Y

cat exp_reusedmp.par

dumpfile=dbaclass_estim.dmp
logfile=dbaclass.log
directory=EXPDIR
tables=DBACLASS.OBJECT_LIST
REUSE_DUMPFILES=Y

At this point, we already have the dumpfile dbaclass_estim.dmp . So the EXPDP job should overwrite this dumpfile.

expdp parfile=exp_reusedmp.par

Export: Release 12.1.0.2.0 - Production on Mon Nov 19 12:53:54 2018

Copyright (c) 1982, 2014, Oracle and/or its affiliates.  All rights reserved.

Username: / as sysdba

Connected to: Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
Starting "SYS"."SYS_EXPORT_TABLE_01":  /******** AS SYSDBA parfile=exp_reusedmp.par
Estimate in progress using BLOCKS method...
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 29 MB
Processing object type TABLE_EXPORT/TABLE/TABLE
Processing object type TABLE_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
Processing object type TABLE_EXPORT/TABLE/STATISTICS/MARKER
. . exported "DBACLASS"."OBJECT_LIST"                    24.69 MB  219456 rows
Master table "SYS"."SYS_EXPORT_TABLE_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SYS.SYS_EXPORT_TABLE_01 is:
  /export/home/oracle/dbaclass_estim.dmp
Job "SYS"."SYS_EXPORT_TABLE_01" successfully completed at Mon Nov 19 12:54:01 2018 elapsed 0 00:00:03

As expected, we didnt received the error – ORA-27038: created file already exists.