Dynamically Concatenating Multiple Columns In Sequence?

I have a requirement where in I have to concatenate the fields based on their sequence given in another table along with respect to their lengths.

eg..

Input 1:

Table A: (below are the fields and their respective values, not all fields will have values)

-----------
KSCHL - ZIC0 (KEY)
KOTABNR - 521 (KEY)
MATNR
KUNNR-->1234567890
LIFNR
VKORG-->a234
PRCTR
KUNRE-->4355325363
LIFRE-->88390234
PRODH
---------

Table BSadIt contains the same fields as in table A and will have sequence number in which the concatenation should happen. The length field(LEN) will have corresponding field lengths(pipe delimited) should be considered in concatenation)

---------
KSCHL - ZIC0 (KEY)
KOTABNR - 521 (KEY)
MATNR
KUNNR-->1
LIFNR
VKORG-->3
PRCTR
KUNRE-->2
LIFRE -->4
PRODH
LEN--> 10|10|4|10

Expected Result:

---------------------
KSCHL - ZIC0 (KEY)
KOTABNR - 521 (KEY)
MATNR
KUNNR1234567890
LIFNR
VKORGa234
PRCTR
KUNRE4355325363
LIFRE0088390234
PRODH
Concat_String12345678904355325363a2340088390234

Note: If the field length given in Table B doesn't match with actual size of the fields then, the field should be filled with 2 left spaces while concatenation.. Eg. In above example say LIFNR value = 88390234(len =icon_cool.gif

then after concat the value should be like below:

12345678904355325363a234 88390234

Note:The fields are not constant..I have around 40 fields like that in which any combination of fields can be possible...eg..

KSCHL - ZIC0 (KEY)
KOTABNR - 521 (KEY)
MATNR -->2
KUNNR--> 4
LIFNR
VKORG-->1
PRCTR
KUNRE
LIFRE --> 3
PRODH

I am not sure which field has the value 1, 2 etc.. and how many fields are forming the combination..It can be sometimes 3/40 fields or it can be 10/40 fields...I have to dynamically get those values and concat...

I can have any number of fields for concatenation..above example is just for 4...it should be dynamic enough to handle any number of fields..