Masking PII columns in Oracle

I am using Oracle 11g R2 on Linux, and I have multiple tables in my database that has got columns that needs to be masked. I have tried the OEM to mask the data as mentioned in the below hyperlink, it worked fine. http://www.oracle.com/webfolder/technetwork/tutorials/obe/em/emgc10205/data_masking/datamask.htm But I couldn't find any blog that gives manual ways to mask data in oracle, like executing packages, functions and so on via SQLPLUS prompt. Could someone please suggest me how else can this be achieved