Installing Application Express with Oracle 10g Express Edition on Ubuntu is as easy as installing on Windows.

I have comprehended the steps to install Oracle Express Edition along with APEX 3.2 in Ubuntu.

UPDATE: The same procedure works for upgrading to APEX 4.0 from APEX 3.2 or directly installing 4.0 over Oracle XE as well.

1) Download Oracle XE universal .deb file from oracle.com

Download apex_3.2.zip from oracle.com

2)  Double click the .deb file and install the package.

then in Terminal window type:
Type:

 sudo /etc/init.d/oracle-xe configure 

Follow the instructions given there to complete the installation of Oracle 10g.

3) Setting the Oracle Path:
Edit your .bashrc file to include the lines:

ORACLE_HOME=/usr/lib/oracle/xe/app/oracle/product/10.2.0/server
PATH=$PATH:$ORACLE_HOME/bin
export ORACLE_HOME
export ORACLE_SID=XE

export PATH

4) UPGRADING TO APEX 3.2
Place apex_3.2.zip in folder /tmp.
In terminal:

cd /tmp
unzip apex_3.2.zip
cd /tmp/apex
sqlplus /nolog 

Type:

connect sys as sysdba

Note: Prompt for password of database admin login
Type:

 @apexins SYSAUX SYSAUX TEMP /i/ 

This will take several minutes for installation.

5) Setting the Images folder
In terminal Type inside /tmp/apex directory:

sqlplus /nolog

In sqlplus:

connect sys as sysdba
@apxldimg.sql /tmp

6) Enable remote http connections:

SQL>

 exec dbms_xdb.setListenerLocalAccess (l_access => FALSE);

Login

URL: http://127.0.0.1:8080/apex

Workspace: Internal

Username: Admin

Password: password

Source:

http://ubuntuforums.org/showthread.php?t=899926

https://help.ubuntu.com/community/Oracle10g

and Apex Documentation

    Here is a simple code for reading the entire contents of a file into a string in PL/SQL using utl_file package.
It iterates through the file, concatenating each line at a time using get_line function.
declare
  f_in utl_file.file_type;
  s_in varchar2(10000);
  string varchar2(32000);

begin
 f_in := utl_file.fopen('SAMPLEDIR','input.txt','R');

   loop
      begin
        utl_file.get_line(f_in,s_in);
        EXCEPTION
          WHEN NO_DATA_FOUND THEN
        EXIT;

        string:= string || s_in;

      end;
   end loop;
 utl_file.fclose(f_in);
end;

 In the above code SAMPLEDIR is a logical entry in the database pointing to a directory which needs to be created before performing any file handling procedures. The following link lets you get started with file handling in PL/SQL in case if you are new to it. http://www.devshed.com/c/a/Oracle/Reading-Text-Files-using-Oracle-PLSQL-and-UTLFILE/1/