selavy / quash

"Quite a Shell" - A really simple shell for the *nix environment.

quash

"Quite a Shell" - A really simple shell for the *nix environment.

1. To compile quash

make

2. To run quash

./quash

3. To run quash with commands inside a file instead

./quash < commands.txt

4. Features in quash 4.1: Run executables 4.1.a: Run executables with an absolute path > /bin/ls 4.1.b: Run executables in PATH Quash will search for the executable in the directories list in the PATH variable (assuming /bin is in PATH) > ls 4.2: Run executables with arguments run an executable as specified in 4.1 and add arguments: e.g. > ls -la 4.3 Set HOME and PATH set HOME=/home/myhomedir separate directories with a ':' set PATH=/usr/local/bin:/bin: 4.4: To exit Quash

   quit exit 4.5 Change directory: cd e.g. > cd .. 4.6 Execute a process in the background Add a '&' at the end of the command e.g. emacs & 4.7 List background processes jobs 4.8 Redirection 4.8.a Input Redirection Use the '<' character followed by a filename to redirect stdin from the given file. e.g. cat < input.txt 4.8.b Output Redirection use the '>' character followed by a filename to redirect stdout to the given file. e.g. ls > out.txt 4.9 Pipe Connect commands together with a pipe e.g. ls | more 4.10 Kill Send a signal to a background process using kill kill To stop a process use: > kill 9 1

Background execution does not work for jobs, kill, set, or cd because it doesn't make any sense to do them in the background (though you can in a bash shell).

The implementation is most easily thought of as a state machine, once a token is recognized it goes into that command's "state". I began a better implementation, using Yacc and Lex, but wasn't able to finish it in time. My implementation of pipes in this version is very convuluted because there are so many global flags that are being set and reset to make the pipe work correctly, and this is why I don't have more than one pipe implemented. In the Yacc and Lex version I have the capability to execute more than one pipe, but I was struggling to figure out how to write the grammar correctly to let me set up the pipes and read the input correctly. The biggest problem with Yacc and Lex is that I don't know how to properly recover from errors--it quits as soon as a malformed input is received.