Functions

• fork : creates a new process
• strtok : Used on solaris to replace strsep (used in your book)
• getenv : returns the string associated with some environment variable
• malloc: memory allocation in C, you may use new if you compile with the g++ compiler
• argv and argc: arguments to programs
• printf: prints output to the console i.e. cout
• scanf: reads input from keyboard i.e. cin or getline

Shell Functionality

• Shell reads commands from keyboard, the <return> tells it to parse the command line for the command and arguments (options and data)
• Shell has to find the command (using PATH)
• Shell creates a new process with fork() to execute the command
• The child process executes the command while the shell waits.
• The program of the child process reads the file with the command, and that program reads the data and performs its duty

Launch Program (Example from Chapter 2)

• The launch program is used as:
• Launch launch_script
• Where launch_script is a file containing a set of commands to execute.
• Launch reads the file, and executes each of the commands in a manner similar to a shell.
• ParseCommand(…) This function uses strsep and is given in your textbook. I have a rewritten version for you to copy from ~hardnett/pub/cis343/lab2/parsecommand.txt

Strategy

1. You need to understand this program first, by typing it in, running it and getting it to work. Then you will be ready to tackle the minishell program.
2. A sample executable of ms can be executed:

% ~hardnett/pub/cis343/demos/ms

Your program should have the same behavior.

3. Use man <functionname> to learn about the C system calls