Please read Writeup Formatting Tips, as it is difficult to understand your intention w/o seeing your input file properly formatted (see the section on <code> tags).

What have you tried? Why do you want to do this in Perl, and do you have any experience with it? This is, after all a help resource and not a code writing service.

For some introductory guidance, you'll probably want to take a look at I/O Operators to see how to read/write files and using substr (or pack for the more adventurous) to reformat your strings. You can likely perform all this in a one-liner using the -pi switches (see perlrun), but I'm guessing that's outside your current experience level. If you post some code, or even pseudo-code, I'll be happy to provide pointers and debug assistance (see How (Not) To Ask A Question).