Part I: Specification for Shell Program
In this assignment you are to implement a basic shell. A shell is a command line
interpreter that accepts input from the user and executes programs on behalf of the user
based on the commands that the user inputs. The line that the user enters commands on is
referred to as the command line. The shell repeatedly prints a prompt on the command
line, waits for the user to enter commands and executes programs. You are to write a
simple Unix-like shell in the C programming language that has these features:
• If your name is xyz then the prompt should be the string xyz>
• Your shell must support I/O redirection. This includes supporting both input and
output redirection in the same command i.e., you should be able to support the
following: sort < f1.txt > f2.txt. However, you can assume that < will appear at most once in the command and that > will appear at most once in the command.
• Your shell must support multiple pipes.
• You do not have to support a command that has both I/O redirection and pipes.
• A built-in command is a command that changes the state of the shell or requests
information about the shell’s state. You should support the following two built-in
o exit: This command is used to terminate the shell.
o history: By default this command will display the last ten commands
issued. If there are fewer then 10 commands then display all previously
• When the user types Ctrl-C the shell should terminate.
Part II: Hints
See the assignment web page
Part III: Tentative Mark Distribution
This section describes a tentative allocation of marks assigned for the desired features.
• Prompt is displayed properly (2 points)
• exit command works properly (3 points)
• history command works properly (10 points)
• Repeatedly be able to read and execute a line with a command that has no
arguments and no pipes (10 points)
• Repeatedly be able to read and execute a line with a command that has arguments
• Repeatedly be able to read and execute a line with a command that has pipes (35
• I/O Redirection (15 points)
• Signal (5 points)