This is a simple Unix shell supporting output redirection and piping of up to three commands. This was written for the operating systems course at the university of Victoria.
In main() we read the .sh360rc and populate the local variables prompt and paths with the first line of .sh360rc and the remaining lines respectively through the use of read_rc().
It is assumed that prompt cannot exceed 10 characters in length and that the each directory contained in .sh360rc will be at most 80 characters in length with a max of 10 directories, one per line.
We then enter an infinite for loop which prompts the user to do something. This can be exited by entering the command exit.
In the simple case of executing a single command, main() tokenizes the user input via regular_tokenize() (only 80 of those input characters will be copied into the input variable, greater than 80 characters may cause undefined behaviour). Then the program gets the path to the binary executable of the command which the user enters via get_exec_path(). Finally, the command is ran using a call to the fork() and execve() system calls which are wrapped in run_command().
If the command entered consists of greater than seven tokens, then Error: Number of arguments cannot exceed 7! is printed to stderr.
If the command entered does not have a binary executable located in one of the directories found in .sh360rc, then command: command not found is printed to stderr.
If the first token of the command is OR then we check to see if the input is of the proper format. The proper format is OR commands -> filename.txt. This is done using a regular expression inside the check_OR_input(). If the command is not properly formatted, then Error: Redirection command not properly formatted! 'OR commands -> filename.txt' is the proper format is printed to stderr.
We then check if the number of tokens passed in is less than 7. OR and -> count as tokens. This is done via OR_tokenize().
If the command entered consists of greater than seven tokens, then Error: Number of arguments cannot exceed 7! is printed to stderr.
If the number of tokens are okay we get the executable path via get_exec_path() and redirect the output via do_output_redirect().
If the first token of the command is PP then we check to see if the input is of the proper format. The proper format is PP commands -> commands or PP commands -> commands -> commands. This is done using a regular expression inside the check_PP_input(). If the command is not properly formatted, then Error: Piping command not properly formatted! 'PP commands -> commands' is the proper format Note: An additional '-> commands' is supported is printed to stderr.
We then check if the number of tokens passed in is less than 7. PP and -> count as tokens. This is done via PP_tokenize()
If the command entered consists of greater than seven tokens, then Error: Number of arguments cannot exceed 7! is printed to stderr.
If the number of tokens are okay we get the executable path via get_exec_path() and pipe the output via control_piping().
control_piping() will choose which piping function to call based on the return value of PP_tokenize().
If there is one arrow (two commands), then do_one_arrow_pipe() is called, if there are two arrows (three commands) then do_two_arrow_pipe() is called.