how to increase sqlplus column output length?

I've just used the following command:

SET LIN[ESIZE] 200

(from http://ss64.com/ora/syntax-sqlplus-set.html).

EDIT: For clarity, valid commands are SET LIN 200 or SET LINESIZE 200.

This works fine, but you have to ensure your console window is wide enough. If you're using SQL Plus direct from MS Windows Command Prompt, the console window will automatically wrap the line at whatever the "Screen Buffer Size Width" property is set to, regardless of any SQL Plus LINESIZE specification.

As suggested by @simplyharsh, you can also configure individual columns to display set widths, using COLUMN col_name FORMAT Ax (where x is the desired length, in characters) - this is useful if you have one or two extra large columns and you just wish to show a summary of their values in the console screen.

This configuration is working for me:

set termout off
set verify off
set trimspool on
set linesize 200
set longchunksize 200000
set long 200000
set pages 0
column txt format a120

The column format definition with the linesize option helped to avoid the truncation at 80 chars.

Try this

COLUMN col_name FORMAT A24

where 24 is you width.

On Linux try these:

set wrap off
set trimout ON
set trimspool on
set serveroutput on
set pagesize 0
set long 20000000
set longchunksize 20000000
set linesize 4000

Additionally to setting the LINESIZE, as LordScree suggested, you could also specify to output to a file, to overcome the problem with the console width. Here's how I do it:

set linesize 15000;
spool myoutput.txt;
SELECT 
...
spool off;