This is Project 2 of CSE-34341-SVS-Spring-2023

• Tram Trinh ([email protected])

The goals of this project are:

• To learn the relationship between the kernel, the shell, and user-level programs.
• To learn how to employ the Unix process management system calls.
• To gain more experience in rigorous error handling.

myshell is a program that is capable of executing, managing, and monitoring user level programs. This program will be similar in purpose and design to everyday shells like bash or tcsh, although the syntax will be slightly different. myshell will be invoked without any arguments, and will support several different commands.

myshell should print out a prompt like myshell> when it is ready to accept input. It must read a line of input, accepting several possible commands:

• list-files
• change-dir
• print-dir
• copy-file
• start-process
• wait-for-any-child
• wait-for-a-child
• run-process
• kill-process
• quit
• exit

The built in list-files command should cause the shell to list the contents of the current directory, displaying each filename, type (use F for file and D for directory) and permission bits (see below) , and size in bytes – roughly the same information as ls -l

For example:

myshell> list-files

D . user[rwx]group[r-x]other[r-x] 0 bytes

D .. user[rwx]group[r-x]other[r-x] 0 bytes

F words.txt user[rw-]group[r--]other[r--] 105 bytes

F myshell.c user[rw-]group[r--]other[r--] 2836 bytes

... and so on ...

The built in change-dir command should cause the shell to change its working directory to the named directory:

myshell> change-dir /tmp

The built in print-dir command should cause the shell to print the current working directory:

myshell> print-dir

/escnfs/home/htrinh

The built in copy-file command should duplicate one file or directory to another:

myshell> copy-file old.c new.c

copy-file: copied 2836 bytes from old.c to new.c

The start-process command should start another program with command line arguments, print out the process number of the running program, and then accept another line of input.

For example:

myshell> start-process cp data.txt copy.txt

myshell: process 346 started

myshell>

The wait-for-any-child command causes the shell to wait for any child process to exit. When this happens, indicate whether the exit was normal or abnormal, along with the exit code or signal number and name, respectively. Display any errors encountered.

For example:

myshell> wait-for-any-child

myshell: process 502 exited normally with status 5

myshell> wait-for-any-child

myshell: process 347 exited abnormally with signal 11: Segmentation fault.

myshell> wait-for-any-child

myshell: No children.

The wait-for-a-child command does the same thing, but waits for a specific child process to exit:

myshell> wait-for-a-child 346

myshell: process 346 exited normally with status 0

myshell> wait-for-a-child 346

myshell: No such process.

The run-process command should combine the behavior of start-process and wait-for-a-child. run-process should start a program, wait for that particular process to finish, and print the exit status.

For example:

myshell> run-process date

Mon Jan 19 11:51:57 EST 2023

myshell: process 348 exited normally with status 0

The kill-process command should kill the process whose pid is given.

myshell> kill-process 346

myshell: process 346 has been killed

myshell> kill-process 346

myshell: unable to kill process 346

After each command completes, the program will continue to print a prompt and accept another line of input. The shell should exit with status zero if the command is quit or exit or the input reaches end-of-file. If the user types a blank line, simply print another prompt and accept a new line of input. If the user types any other command, the shell should print a reasonable error message:

myshell> bargle ls -la

myshell: unknown command: bargle