fvera002 / rshell

HW0 CS100 Spring 2015

#Rshell HW0 CS100 Spring 2015

##Authors and Contributors ######Author

Fernando Donizete Verago Junior

######Contributors

Isadora Maria Mendes de Souza (cp.cpp)

Andrew So (rm.cpp and mv.cpp)

##General Information ####HW0: rshell This is an implementation of a command shell in which users can input either a simple command or multiple commands at a single entry by using connectors.

• this is an example of a single command:

  ls

• this is an example of mutiple commands separeted by the connector comma:

  ls ; pwd ; echo test

There are only 3 conectors supported by rshell:

• && if a command is followed by &&, then the next command is executed only if the first one succeeds
• || if a command is followed by ||, then the next command is executed only if the first one fails
• ; if a command is followed by ;, then the next command is always executed

A command can have mutiple arguments, also known as flags. For example:

ls -a -l -R

Users can also include comments in a entry by using the character #:

ls -a #this is a comment

When mixing up connectors in a single entry, rshell group the commands from left to right. For example:

echo a || echo b && echo c && echo d

This command would return:

a
c
d

Since echo a succeed, echo b is not executed. Then echo c is run because the previous command failed. Finally, echo d is executed also because echo c succeed.

####HW1: ls The ls feature was built in order to behave exactly as GNU implementation does, but with some limitations. This behavior can be seen in the man page of ls. The main point that this hw1 ls implementation differs from the actual GNU's ls is that it only supports the flags -a, -l and -R. For example:

ls -a -l -R

The flags can be placed in different orders and also together:

ls -l -a -R

ls -lRa

ls -al -R

There is also the case in which you may want to include optional files to your command. This implementation also handles that:

ls -l file1.txt file2.doc

Again, the order in which the flags appear in your command line does not matter:

ls file1.txt file2.doc -l

####HW2: rshell piping The first version of rshell was not able to handle piping and I/O reirection. Now that these features are available, commands like ls -l > files.txt and ls -laR | grep Makefile will work just like an UNIX bash implementation.

Also, these commands can be mixed up together:

ls -laR | grep Makefile > ls_make.txt

This last command would run ls -laR | grep Makefile and redirect its output to the file ls_make.txt.

Just like bash, when chaining multiple redirection commands together (e.g. echo test > f1 > f2 > f3), even though rshell will create, open and close all files in the chain, only the last one will contain the output (i.e. only f3 will contain test).

However, when mixing up multiple input redirections with other input/output redirectins (e.g. ./a.out < inputFile > output1 > output2), rshell has a different aproach from Unix bash implementation. It echos out to the first output file in the chain (i.e. output1).

####HW3: rshell signals and cd command This version implements the feature to handle ^C signals from the user so that rshell does not exit; instead, it send the SIGINT signal to the foreground process. It means that if you run a program through rshell that goes into a infite loop, now you are able to interrupt this program by pressing ^C (aka. control key + C).

Additionally, now rshell is able to run the cd command in various forms.

• cd by itself changes the current working directory to the HOME directory.
• cd <PATH> changes the current working directory to the desired PATH.
• cd - changes the current working directory to the previous working directory.

For example, if I am working on ~/dir1 , then I run cd wdir2/wdir3, I will be at ~/dir1/wdir2/wdir3. Then if I run cd - it will take me back to the previous directory I was at, which is ~/dir1.

##Installation ####Installation HW0: rshell To be able to install and run the program, it's necessary to clone the repository, run the make command, then finally run rshell that is going to be located in the bin folder. It means that for each homework the following commands would run the needed executable, just differing in the commented part:

$ git clone  https://github.com/fvera002/rshell.git
$ cd rshell
$ git checkout hwn  #replace n by de desired homework number (e.g. hw0, hw1...)
$ make
$ bin/rshell        #for hw1 instead of rshell the desired file would be bin/ls

Upon running, the program will display a prompt waiting for an entry:

logged_user@machine_name123 ~path/from/home/directory $

The same prompt will be displayed every time the program is done executing commands. There is a built in command that can be used to quit the program:

exit

It can also be used together with other commands and connectors. For instance:

ls -l ; pwd; exit

Therefore, this last example would run ls -l, then pwd, so finally it would exit the program.

Bugs and Limitations

####Bugs HW0: rshell

• Running bin/rshell by redirecting its input would not work properly.

  Do not run:
  bin/rshell < tests.txt
  

• It's possible to run a number of commands in a single input; however, there is a limitation of characters accepted depending on the environment. In most of the tests this limit was 4094 characters per entry.

####Bugs HW1: ls

• Output does not line up exactly as it should when running ls in a folder with many files.

• The order in which files are displayed is not matching GNU's implementation when files have similar names, such as ls.cpp and ls2.cpp.

####Bugs HW2: rshell piping.

• Chaining multiple input redirections does not match UNIX bash behavior. Further explanation about this is found above on the overview section.