Project 1: The Shell - Part 2
Starting from the command table produced in Part 1, in this part you
will execute the simple commands, do the file redirection, piping and
if necessary wait for the commands to end.
- For every simple command create a new process using fork()
and call execvp() to execute the corresponding executable. If the
_background flag in the Command struct is not set then your shell has to
wait for the last simple command to finish using waitpid().
Check the manual pages of fork(), execvp(), and waitpid().
Also there is an example file that executes processes and does
redirection in cat_grep.cc. After
this part is done you have to be able to execute commands like:
ls -al
ls -al /etc &
- Now do the file redirection. If any of the input/output/error is
different than 0 in the Command struct, then create the files, and use dup2()
to redirect file descriptors 0, 1, or 2 to the new files. See the
example cat_grep.cc to see how to do
redirection. After this part you have to be able to execute commands
like:
ls -al > out
cat out
ls /tttt >& err
cat err
cat < out
cat < out > out2
cat out2
ls /tt >>& out2
">& file" redirects both stdout and stderr to file.
">>& file" append both stdout and stderr to file.
">> file" appends stdout to file.
- Now do the pipes. Use the call pipe() to create pipes that
will interconnect the output of one simple command to the input of the
next simple command. use dup2() to do the redirection. See the
example cat_grep.cc to see how to
construct pipes and do redirection. After this part you have to be able
to execute commands like:
ls -al | grep command
ls -al | grep command | grep command.o
ls -al | grep command
ls -al | grep command | grep command.o > out
cat out
- Your shell has to ignore ctrl-c. When ctrl-c is typed, a signal
SIGINT is generated that kills the program. There is an example
program in ctrl-c.cc that tells you how to ignore SIGINT. Check the
man pages for
sigset.
- You will also have to implement also an internal command called
exit that will exit the shell when you type it. Remember that
the exit command has to be executed by the shell itself without
forking another process.
myshell> exit
Good bye!!
csh>
- Implement the cd [ dir ] command. This command changes the
current directory to dir. When dir is not specified, the
current directory is changed to the home directory. Check "man 2
chdir".
-
When your shell uses a file as standard input your shell should not
print a prompt. This is important because your shell will be graded by
redirecting small scripts into your shell and comparing the
output. Use the function isatty() to find out if the input comes from
a file or from a terminal.
Submission Instructions
The deadline of this part of the project is March 31, 2005,
before class. Follow these instructions to submit.
1. Login to daruma.cs.georgetown.edu.
2. cd to shell-src and type make clean
3. Type make to make sure that your shell is build correctly.
4. Type make clean again.
5. cd one directory above shell-src by typing "cd .."
6. Create a tar file named <user_name>.tar, where <user_name>
is your daruma.cs.georgetown.edu login, by typing
tar -cf <user_name>.tar shell-src
7. Gzip the tar file by typing
gzip <user_name>.tar
8. Since this timestamp will be used to verify whether the work was
completed on time or not, you should set the permissions on the file you
submitted to make sure that the file timestamp is not changed. So this
by typing:
chmod a-w <user_name>.tar.gz
9. Mail the gzipped tar file to clay at cs dot georgetown dot edu as an attachment.
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