Assignment

1. Write a program that accepts one line of standard input at a time.
   • It should break that line into parts based on whitespace.
   • It should use the first value from the resulting iterator as the command, and the remaining values as the arguments.
   • If the command is the word exit, the shell should exit.
   • Otherwise, it should spawn a new process to execute the named command.
   • Make sure to include its command-line arguments.
2. Using the cd program fails to change the directory, as the directory change only affects the child process. Add a built-in cd instruction that changes the current working directory of the shell process itself. Its argument is the target directory. If no argument is supplied, it should change to the user's home directory, which is accessible through the HOME environment variable.
3. The * character is a pattern-matching wild card character. It matches zero or more arbitrary characters. For every command-line argument containing this character, replace it with one or more command-line arguments that are all valid matches from the file system. The updated command-line arguments should be what gets passed to the child process. Here is an example:

   bash$ ls
   hello.py	one.txt		two.txt
   bash$ ls *.txt
   one.txt		two.txt
   bash$ ls *.py
   hello.py
   bash$ 
   

   For this assignment, you need only be concerned with pattern-matching files in the current directory. You may also assume that there will be no more than one occurrence of the pattern-matching character.

Grading

Acknowledgement