pseudo.txt

#includes
function declarations

while true :
	reap children processes (catch possible zombie processes)

	get { hostname, username, current directory, $OLDPWD(NULL to start) }
	print username@hostname prompt
	
	create 3 arg lists (allocate mem properly, initialize to NULL)
	read sommand line input 
		parse out whitespace,
		do input error handling (malformed/ambiguous commands)
		fill first argslist with full command line
	check for IOacct/background process commands, adjust first argslist
	
	if cmd = built-in (cd, ioacct, exit) :
		if cd : 
			chdir(), handle special cases (-, ~, blank, &)
		if exit[n] : 
			reap child processes, return n;
		
	else :
		parse out possible pipes in first argslist
			fill second and third argslists with piped commands

		if no pipes:
			parse first arglist for redirects, adjust array, store redirect stream
			search PATH for cmd

			child = fork()
			if child == 0 (inside child) :
				check redirects:
					if in redirect, open file RDONLY, dup STDIN, close
					if out redirect, creat() file 0644 perms, dup STDOUT, close
					if append redirect, open file WRONLY|APPEND, dup STDOUT, close
				execv(cmd path, args)
			else if background:
				waitpid(-1, (int *)NULL, WNOHANG);
			else if ioacct:
				read from proc/[pid]/io file while waitpid(WNOHANG) == 0
				print bytes read/written
			else (inside parent):
				waitpid(-1, (int *)NULL, 0)

		if 1 pipe:
			create pipe int array pipefd[2], call pipe()
			parse second argslist for redirects
			
			child = fork()
			if child == 0 (inside second argument):
				set input fd to pipefd[0], close fd's
				check redirects:
					if in redirect, open file RDONLY, dup STDIN, close
					if out redirect, creat() file 0644 perms, dup STDOUT, close
					if append redirect, open file WRONLY|APPEND, dup STDOUT, close
				execv(2nd cmd path, args)
			else (in parent):
				child2 = fork()
				if child == 0:
					set output fd to pipefd[1], close fd's
					execv(1st cmd path, args)
			close pipes
			call waitpid(-1, (int*)NULL, 0) on both processes

		if 2 pipes:
			create pipe in array pipefd[4], call pipe twice
			parse third arglist for redirects

			child = fork()
			if child == 0 (1st cmd):
				set output to pipefd[1], close fd's
				execv(1st cmd path, args)
			else:
				child2 = fork()
				if child2 == 0 (2nd cmd):
					set input fd to pipefd[0], output to pipefd[3], close fd's
					execv(cmd path 2, args)
				else:
					child3 = fork()
					if child3 == 0 (3rd cmd):
						set input to pipefd[2], close fd's
						do redirect fd dup2's
						execv(cmd path 3, args)
			close pipes
			call waitpid(-1, (int*)NULL, 0) on all 3 processes