First step is to add Oracle repository to your packages repository list. In your /etc/apt/sources.list, insert:

deb http://oss.oracle.com/debian unstable main non-free

Then you have to update your local packages index and install the oracle-xe-client packages. The Oracle client package is 25MB fat, so it make take some time to download. Be also warned that the installation procedure checks that you have at least 500MB of RAM and 1GB of swap space. I only have 996MB of swap, the installer said it was not enough and that the procedure had failed, but it works perfectly, so I suppose it was just a warning.

$ sudo apt-get update
$ sudo apt-get install oracle-xe-client

In order to use sqlplus, the Oracle command client, you need to set some environment variables. Copy paste these variables in your ~./.profile . Here follows what I've found in the /usr/lib/oracle/xe/app/oracle/product/10.2.0/client/scripts/sqlplus.sh file:

export ORACLE_HOME=/usr/lib/oracle/xe/app/oracle/product/10.2.0/client
export NLS_LANG=`$ORACLE_HOME/bin/nls_lang.sh`
export SQLPATH=$ORACLE_HOME/sqlplus
export PATH=$ORACLE_HOME/bin:$PATH

By default, the installer didn't create the well known tnsnames.ora configuration file. So, I create /etc/tnsnames.ora by hand, with the following content:

TALEND =
   (DESCRIPTION =
      (ADDRESS_LIST =
         (ADDRESS = (PROTOCOL = TCP)(HOST = talend-dbms)(PORT = 1521))
      )
      (CONNECT_DATA =
         (SERVICE_NAME = TALEND)
      )
   )

The final step is to try sqlplus:

$ sqlplus root@TALEND
[...]
SQL> select count(*) from sales;
 
  COUNT(*)
----------
     10000
 
SQL>