leelu:

If all records are updated, then read only one record at a time, and perform your substitution only on the first record. You don't show code, so I can't tell you exactly what you're doing wrong. (You could be reading in the entire file and doing the substitution globally, you could be substituting in a loop. Hard to say without seeing the code.)

...roboticus

When your only tool is a hammer, all problems look like your thumb.