The following are implementation requirements and recommendations for your shell program:
(Required) Your program should be modular at the function level. Define small functions, each of which does a single well-defined job.
(Required) Your program should be modular at the source code file level. Define interfaces and implementations, thus splitting your program into multiple files.
(Required) Define stateless modules as appropriate. A stateless module is one that does not have any associated data. For example, your Str module from Assignment 2 is a stateless module; it consists of a group of related functions, but does not encapsulate any data.
(Required) Define abstract objects and abstract data types as appropriate, thus encapsulating data structures with functions.
(Recommended) Your program may use the DynArray ADT (from early precepts). The source code is available through the course web pages, and also in the /u/cos217/Assignment7 directory on nobel.
(Required) If the user specified a command-line argument to your program, then your program should interpret the command-line argument as the name of a configuration file. It is not an error for the user to omit the command-line argument. If the user specifies more than one command-line argument, then the program should print an error message and exit.
(Required) If the configuration file exists and is readable, then your program should read and interpret all commands from that file. If the configuration file does not exist or is not readable, then your program should write an error message. In either case, your program then should read and interpret all commands from stdin.
If your program does not support reading a configuration file, or does not interpret commands from that file, then it will fail all of our tests. In that unfortunate circumstance, the grade would be reduced substantially.
(Required) Your program should print the commands from the configuration file. That is, immediately after your program reads a command from the configuration file, it should print its "% " prompt and that command to stdout. In that manner your program should generate a transcript that shows each command of the configuration file, followed by the output that results from executing that command.
If your program does not print the commands of the configuration file to stdout, then it will be difficult to interpret the transcript. In that unfortunate circumstance, the grade would be reduced.
(Required) Your program should not print the commands from stdin. That is, when your program reads a command from stdin, it should not print that command to stdout.
(Required) Your program should make no assumptions about the maximum number of characters in each line read from the configuration file or from stdin, the maximum length of the name of the given command, the maximum length of any of the command-line arguments of the given command, or the maximum number of command-line arguments of the given command.
(Recommended) Your program should define the readLine function given in the dfa.c precept example program, and should read each input line by calling that function.
(Required) A programmer error is one that could not possibly be caused by user input. Your program should detect a programmer error via an if statement, report the error via a descriptive error message written to stderr, and then exit with EXIT_FAILURE as the status code.
(Required) Invalid function parameter is a special-case programmer error. Your program should call the assert macro to handle that error. Of course the assert macro will detect the error, report the error by writing a message to stderr, and exit.
(Required) A user error is one that could be caused by user input. Your program should detect a user error via an if statement, and report the error via a descriptive error message written to stderr. Then your program should reject the offending input line and continue execution.
(Required) In general heap exhaustion (that is, a failed call of malloc, calloc or realloc) could be caused by user input, and so should be treated as a user error. However in this particular program (1) there is no reasonable user input that could cause heap exhaustion, and (2) if heap exhaustion does occur, then there is no reasonable way for your program to recover from it and continue execution. So your program should treat heap exhaustion as a programmer error. That is, your program should detect heap exhaustion via an if statement, report the error via a descriptive error message written to stderr, and then exit with EXIT_FAILURE as the status code.
(Required) Your program's error messages should begin with "programName: ", where programName is your program's argv[0]. Note that the name of your program is not necessarily "ish"; the user might have renamed the executable binary file to something other than "ish".
(Required) After a failed call of a function that sets the errno variable, your program should call the perror or strerror function to print an appropriate error message to stderr.
(Recommended) Implement your lexical analyzer as a deterministic finite state automaton.
(Required) Your program should call the isspace function to identify white-space characters.
(Recommended) Create some temporary code that prints the token list created by your lexical analyzer. Do not proceed to subsequent phases until you test your lexical analyzer thoroughly.
(Recommended) Test your lexical analyzer by making sure that it handles these example input lines properly:
| INPUT LINE | TOKEN ARRAY |
one |
one |
123 |
123 |
one123 |
one123 |
123one |
123one |
@#$%^&*() |
@#$%^&*() |
' |
' |
one two |
one two |
one two |
one two |
one two |
one two |
one > |
one > |
one> |
one > |
>one |
> one |
"one" |
one |
">" |
> (an ordinary token) |
"one two" |
one two |
one"two" |
onetwo |
"one"two |
onetwo |
"one |
ERROR |
one"two |
ERROR |
(Recommended) Your program's lexical analyzer should represent tokens so that the difference between quoted and unquoted special characters is adequately captured. For example, these two commands are very different, and that difference should be captured at the lexical analysis phase:
echo one > two echo one ">" two
(Recommended) Your program should do as much validation of the command as possible at the syntactic analysis phase. The more error checking you do during the syntactic analysis phase, the less must be done during the (more complicated) execution phase.
(Recommended) Create some temporary code that prints the command created by your syntactic analyzer. Do not proceed to subsequent phases until you test your syntactic analyzer thoroughly.
(Recommended) Test your syntactic analyzer by making sure that it handles these valid and invalid example input lines properly:
| INPUT LINE | VALID/INVALID |
cat |
Valid |
cat file1 |
Valid |
cat < file1 |
Valid |
cat > file1 |
Valid |
cat < file1 > file2 |
Valid |
cat > file1 < file2 |
Valid |
cat file1 > file2 |
Valid |
cat > file2 file1 |
Valid |
< file1 |
Invalid |
cat file1 < |
Invalid |
cat file1 > |
Invalid |
cat file1 > file2 > file3 |
Invalid |
cat < file1 < file2 |
Invalid |
(Required) Your program should call fflush(NULL) before each call of fork to clear all I/O buffers.
(Required) Your program should call the setenv function to implement the setenv shell built-in command.
(Required) Your program should call the unsetenv function to implement the unsetenv shell built-in command.
(Required) Your program should call the chdir function to implement the cd shell built-in command.
(Required) Your program should call exit(0) to implement the exit shell built-in command. Or, implement the exit command by returning 0 from the program's main function.
(Required) Your program should call the signal function to install signal handlers.
(Required) Your program should call the alarm function to control handling of SIGQUIT signals.
(Required) Your program should use the SIG_IGN and SIG_DFL arguments to the signal function, as appropriate.
(Required) Your program should call the sigprocmask function near the beginning of the main function to make sure that SIGINT, SIGQUIT, and SIGALRM signals are not blocked.