text file reformatting

[iwawi]

I have this fixed width data file (data.txt) which I would like to
reformat. Data is something like this, with hundreds of rows and
columns, every row finishes to END:

PRJ01001 4 00100END
PRJ01002 3 00110END
PRJ01003 3 00120END
PRJ01004 2 00130END
PRJ01005 1 00140END
PRJ01006 1 00150END
PRJ01007 3 00160END

I would like to pick only some columns to a new file and put them to a
certain places (to match previous data) - definition file (def.csv)
could be something like this:

VARIABLE	FIELDSTARTS	FIELD SIZE	NEW PLACE IN NEW DATA FILE
ProjID	;	1	;	5	;	1
CaseID	;	6	;	3	;	10
UselessV  ;	10	;	1	;
Zipcode	;	12	;	5	;	15

So the new datafile should look like this:

PRJ01    001       00100END
PRJ01    002       00110END
PRJ01    003       00120END
PRJ01    004       00130END
PRJ01    005       00140END
PRJ01    006       00150END
PRJ01    007       00160END

If the datafile was as narrow as in this demofile, I would simply use
notepad to fix this, but there are more
than 100 variables I should pick and replace...

I'm missing the logic here - how it should be done?