如何在shell脚本文件中隐藏连接到oracle数据库的密码？

;;;
Export: Release 11.2.0.4.0 - Production on Tue Jun 13 04:00:02 2017

Copyright (c) 1982, 2011, Oracle and/or its affiliates.  All rights reserved.
;;;
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
;;; Legacy Mode Active due to the following parameters:
;;; Legacy Mode Parameter: "indexes=TRUE" Location: Command Line, ignored.
;;; Legacy Mode Parameter: "statistics=none" Location: Command Line, ignored.
;;; Legacy Mode has set reuse_dumpfiles=true parameter.
Starting "SZD_BASE_V2"."SYS_EXPORT_SCHEMA_01":  /********@base schemas=szd_base_v2 directory=expdp parallel=3 dumpfile=expdp_szd_base_v2_20170613040001_%U.dmp logfile=expdp_szd_base_v2_20170613040001.log reuse_dumpfiles=true
Estimate in progress using BLOCKS method...
Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
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