Shell Programming and Scripting

Oracle /Unix
There is one update script, which I am directly passing like
update XX_NET_IMPORT_DATA
set file_id=xx_data_files_s.CURRVAL
WHERE FILE_ID IS NULL;

There is another insert in the script, and found these are giving two different values.

select xx_data_files_s.nextVAL is have value 100 where xx_data_files_s.CURRVAL is having other value, which it should be 100-1 =99 where incremental is 1.

Can any one tell why this happen..
Do we need to get the value from somewhere and then reset??

I dont understand the question at all. CURRVAL should have the current value of the sequence, whereas NEXTVAL should have the next value on it. Is that what you mean ?