[GTALUG] Processing a binary file with a shell script

Hello All, I am writing a bourne shell script, to read a binary file as input and take action depending on the contents of the file. The file is a mixture of ASCII and binary codes (such as ASCII filed lengths and flags). I have the processing already done in C. I would like to convert it to a bourne shell. Does anyone have any suggestions on what combination of tools I may be able to use?