notes.txt

File redirection (< and >)
	- dup2 copies file descriptors

	fd = open(file)
	dup2(fd, 0) //0 for stdin, 1 is stdout, 2 is stderr

	fd = open("fred.txt", O_RDONLY);

	fork
	if kid
		for each arg
			if arg is ">"
				fdout = open for writing
				error check
				remove 2 args from the list
			if arg is "<"
				fdin = open for reading
				error check
				remove 2 args from the list

		build the argument list
		dup2(fd, 0)
		for p in PATH
			exec
		print error
		exit(3)


Good reference: https://stackoverflow.com/questions/8082932/connecting-n-commands-with-pipes-in-a-shell
Piping
	- piping must be continuous
	- pipe is a system call in linux
	- MAKE SURE TO PIPE BEFORE FORK
	- both sides have both file descriptors
		reader must close write end of pipe (pipefd[1])
		writer must close read end of pipe  (pipefd[0])

		1. close
		2. dup2
		3. exec

	For example, "ls | wc" would go like this:
	if arg is "|"
		pipe()
		fork() //we are now at 3 copies of the program (child forks itself on pipe)
		if kid2 "ls"
			close the read end (pipefd[0])
			dup2(pipefd[1], 1) //stdout
			exec "ls"

		if parent "wc"
			close the write end (pipefd[1])
			dup2(pipefd[0]) //stdin
			exec "wc"



using $ variables
	-getenv() is allowed for anything besides PATH

	if arg is $
		replace with getenv(that arg without the $)

; is done before the fork

	if ;
		do everything before ;
		do everything after ;