This one should: Create a child process If it is the child process then Open FILENAME for reading and tell the process that that file its standard input. Tell the process that it should use the file descriptor for talking to the client as its standard output. Do this: char awkCmd[BUFFER_LEN]; snprintf(awkCmd, BUFFER_LEN,"{print $%d}",columnIndex); which composes the command to give to awk Run /usr/bin/awk with awkCmd as the command line argument If any of these fail then it should send STD_ERROR_MSG of length STD_ERROR_MSG_LEN to the client and do exit(EXIT_FAILURE) Meanwhile the parent should wait for the child process to finish.