CSC415 San Francisco State University Building Simple Shell Project CSC 415 – Building Simple Shell Project 3 Total Points: 150 Points Description For this

CSC415 San Francisco State University Building Simple Shell Project CSC 415 – Building Simple Shell
Project 3
Total Points: 150 Points
Description
For this assignment you will implement your own Shell or Command Line Interpreter (e.g.
to replace /bin/bash for simple interactions with the Linux Kernel.). Your shell will be
character-oriented, and will fork off processes to execute user entered commands.
Your shell should read lines of user input into a 256-byte buffer, then parse and execute
the commands (be sure to clear the buffer between successive commands!) It should be
possible for the user to specify the command to execute by giving an absolute path to
the file containing the executable (e.g. ./hw1); or to use path expansion to locate the file
containing the executable by using the environment PATH variable to construct a series of
absolute paths and executing the first file found in this way (note that the execvp() command
performs this processing automatically, you do not need to program this yourself!) Your
code should parse the input string and separate it into a collection of sub-strings (stored in
myargv[]) along with a count of the number of strings encountered (stored in myargc). Note
that piped commands will require multiple argc/argv instances!
Shell Requirements
Your shell should support the following functions (Note : this does not mean your shell
should implement LS but rather the ability to execute the LS program):
• Must maintain myargc and myargv for commands you will fork. In some cases you
may need multiple instances for pipe commands.
• The commands cd and pwd must be implemented in your shell.
• Execute a single command with up to four command line arguments (including command line arguments with associated flags). For example:
– myshell>> ls –l
– myshell>> cat myfile
– myshell>> ls –al /usr/src/linux
• Execute a command in background. For example:
– myshell>> ls -l &
– myshell>> ls –al /usr/src/linux &
1
• Redirect the standard output of a command to a file. For example:
– myshell>> ls -l > outfile
– myshell>> ls -l >> outfile
– myshell>> ls –al /usr/src/linux > outfile2
– myshell>> ls –al /usr/src/linux >> outfile2
• Redirect the standard input of a command to come from a file. For example:
– myshell>> grep disk > grep linux > ls –al /usr/src/linux | grep linux
– myshell>> ls -la | wc -l
• Execute the cd and pwd commands
– myshell>> cd some path
– myshell>> pwd
**NOTE** That in most Linux distros CD and PWD are not a program like ls but
rather they are shell built-ins. Built-ins are shell commands that are implemented in the
shell and not some external binary. For giving your shell the cd and pwd commands, you
need to implement these functions in the shell with your code, even if it is provided by your
OS. This can be done with the chdir() and getcwd() functions in unistd.h
Suggested implementation strategy to implement a shell with multiple command line arguments (using iterative refinement):
– Implement your shell to simply initialize your shell, display a prompt, read in user
input and print it back to the console.
– Add functionality to your shell to parse user input setting the correct values for myargv
and myargc. Once parsed, print myargv and myargc to the console. Note that myargvs
need to be null terminated for the exec commands to interpret them correctly.
– Add functionality to your shell to execute simple shell commands. Start with commands like ls, then commands with options like ls -la /home.
2
– Add functionality to shell to execute input and output redirection. It is required to
implement >, >>, and >
NEW PROMPT:
? myshell ~/ >>
? myshell ~/hw3 >>
? myshell ~/hw3/build >>
? myshell /etc >>
? myshell /etc/apach2 >>
DO NOT hard code the home path to your computer, you need to detect the home
path of the computer your shell is executing on. Make sure ~/ is printed in all correct
situations.
• ( 30 – Points) Add the functionality to your shell to store a history of all commands
executed. This includes the ability to scroll through this history as well and rerun
previously entered commands. See your basic Linux shell for examples. This also
requires the use of the up and down arrow keys to scroll through the list. Use of
readline header files IS NOT ALLOWED
3
What to submit
1. source code in myshell.c
2. updated README.md with required fields filled out.
How to submit
• git add .
• git commit -m ” message”
• git push
4 CSC 415 – Building Simple Shell
Project 3
Total Points: 150 Points
Description
For this assignment you will implement your own Shell or Command Line Interpreter (e.g.
to replace /bin/bash for simple interactions with the Linux Kernel.). Your shell will be
character-oriented, and will fork off processes to execute user entered commands.
Your shell should read lines of user input into a 256-byte buffer, then parse and execute
the commands (be sure to clear the buffer between successive commands!) It should be
possible for the user to specify the command to execute by giving an absolute path to
the file containing the executable (e.g. ./hw1); or to use path expansion to locate the file
containing the executable by using the environment PATH variable to construct a series of
absolute paths and executing the first file found in this way (note that the execvp() command
performs this processing automatically, you do not need to program this yourself!) Your
code should parse the input string and separate it into a collection of sub-strings (stored in
myargv[]) along with a count of the number of strings encountered (stored in myargc). Note
that piped commands will require multiple argc/argv instances!
Shell Requirements
Your shell should support the following functions (Note : this does not mean your shell
should implement LS but rather the ability to execute the LS program):
• Must maintain myargc and myargv for commands you will fork. In some cases you
may need multiple instances for pipe commands.
• The commands cd and pwd must be implemented in your shell.
• Execute a single command with up to four command line arguments (including command line arguments with associated flags). For example:
– myshell>> ls –l
– myshell>> cat myfile
– myshell>> ls –al /usr/src/linux
• Execute a command in background. For example:
– myshell>> ls -l &
– myshell>> ls –al /usr/src/linux &
1
• Redirect the standard output of a command to a file. For example:
– myshell>> ls -l > outfile
– myshell>> ls -l >> outfile
– myshell>> ls –al /usr/src/linux > outfile2
– myshell>> ls –al /usr/src/linux >> outfile2
• Redirect the standard input of a command to come from a file. For example:
– myshell>> grep disk > grep linux > ls –al /usr/src/linux | grep linux
– myshell>> ls -la | wc -l
• Execute the cd and pwd commands
– myshell>> cd some path
– myshell>> pwd
**NOTE** That in most Linux distros CD and PWD are not a program like ls but
rather they are shell built-ins. Built-ins are shell commands that are implemented in the
shell and not some external binary. For giving your shell the cd and pwd commands, you
need to implement these functions in the shell with your code, even if it is provided by your
OS. This can be done with the chdir() and getcwd() functions in unistd.h
Suggested implementation strategy to implement a shell with multiple command line arguments (using iterative refinement):
– Implement your shell to simply initialize your shell, display a prompt, read in user
input and print it back to the console.
– Add functionality to your shell to parse user input setting the correct values for myargv
and myargc. Once parsed, print myargv and myargc to the console. Note that myargvs
need to be null terminated for the exec commands to interpret them correctly.
– Add functionality to your shell to execute simple shell commands. Start with commands like ls, then commands with options like ls -la /home.
2
– Add functionality to shell to execute input and output redirection. It is required to
implement >, >>, and >
NEW PROMPT:
?
?
?
?
?
myshell
myshell
myshell
myshell
myshell
~/ >>
~/hw3 >>
~/hw3/build >>
/etc >>
/etc/apach2 >>
DO NOT hard code the home path to your computer, you need to detect the home
path of the computer your shell is executing on. Make sure ~/ is printed in all correct
situations.
• ( 30 – Points) Add the functionality to your shell to store a history of all commands
executed. This includes the ability to scroll through this history as well and rerun
previously entered commands. See your basic Linux shell for examples. This also
requires the use of the up and down arrow keys to scroll through the list. Use of
readline header files IS NOT ALLOWED
3
What to submit
1. source code in myshell.c
2. updated README.md with required fields filled out.
How to submit
• git add .
• git commit -m ” message”
• git push
4

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