Simple string modifying program from file in C -- GCC Compatible

I would like a simple program that operates from the Linux command line that can modify a series of strings from a text file, and write the output to a separate text file. The strings that are to be modified will contain alphanumeric characters and will be unique among the other strings in the file, and the editing function of the program will either prepend a string to all strings in the file, or append a string to all strings in the file. The format of the output file should be: originalString=[prependedString]originalString[appendedString]; The file names will be input and output.