To append the standard output from a command to a file use two >> (greater than) symbols followed by the name of the file. If the file does not exist it is created. For example:

   cat part1 part2 part3 part4 >>chpt2

This reads files part1 through part4 in turn and appends them to the file chapt2. The contents of part2 are appended to part1 nd so on.