Shell Programming and Scripting

Hi Everybody,
I have an layout file like below

Code:

f1 1 char 10,
f2 11 char 2,
f3 13 char 1,
lineend 14 char 1

Their I need to add a new field which would be like

Code:

f5 char 3,
f6 char 2

The o/p should be

Code:

f1 1 char 10,
f2 11 char 2,
f3 13 char 1,
f5 14 char 3,
f6 17 char 2
lineend 14 char 1 /* Note this should be the last field. */

Now my requirement is , I need to automate this process.
i.e the new field addtion f5 and f6 should be automated and the field name data type and the length will be given in a text file. We need to read that file and modify the layout. Can anyone help me how to approach this?

Note : For the new fields to be added, the spaces in between fields should be similar to the old fields.