First you need toc chk is it possible to have a combination of lower and upper letter for field names.If not you can adopt the following procedure.
Declare a structure of above format.
read the input file into the Structure.For all the field names you can find the starting letter using SUBSTR option.if it is lower then find the length of the string and replace with lower case letters.
ex:- let us take the masking for 'ramaaaa'
SUBSTR(FIELDNAME1,1,1) will be 'r' then
Length(Fieldname1) will be '7' so you write 'abcdefg'
like this you can do for reaminig field names as well as 'field values'