wednesday 1/26 - Basic Unix -
Directory structure
	Directories
		special directories
			.
				Current directory
			..
				Parent directory
			/
				Root directory
	Files
		blocks/k
			A block is typically 512bytes (1k = 2 blocks)
			-k to many commands shows 1k vs blocks.
		Inodes
			Pointers to file address(es)

	Interaction
		Manipulation
			mkdir <directory>
				-p [creates all parent directories]
			rmdir <directory>
				-p [removes all empty parent directories]
			mv <file(s)/dir(s)> <destination file/dir>
				-i [ask for each potential overwrite]
				-f [will not ask, will overwrite]
			cp <source file(s)/dir(s)> <dest file/dir>
				-i [ask for potential overwrite]
				-p [preserve file permissions/owner]
				-r [recursively]
				-R [recursive, replicate pipes]
				vs 'tar' for links
			rm <file(s)/dir(s)>
				-i [ask for each file]
				-f [do not ask for anything]
				-r [recursive downwards]
				"rm -r *" or "rm -rf *"	
			ln <source file/dir> <destination in current dir>
				ln expects you to be in the directory
					for the target
				-s [create symbolic link:
					Special file that lists the location
					of the specified directory entry.
					Can point to non-existant location.
					Required for directories on most systems]
		Viewing
			ls
				-s [list sizes]
				-k [some ls's list 1024byte instead of 512/block]
				-C [columnar]
				-F [show special status:
					/ for directory
					* for executable
					@ for symlink]
				-a [show files starting with .]
				-A [some ls's list start with ., not ./..]
				-l [long listing format]
				-i [list inode]
			cd <directory>
			pwd
	
			"Current working directory"
			df
				-k [list in 1024bytes vs 512byte blocks]
			du
				-k [list in 1024bytes vs 512byte blocks]
				-s [sum of selected items/dirs]
			cat <file(s)>
			more <file(s)>
				lists in chunks
			head <file(s)>
				Lists start of files
			tail <file(s)>
				Lists ends of files
				-f [stay at end and show additions]
Other commands
	su
		Without arg, attempts to become root
		with username, attempts to become that user
		su - <name>
			will attempt to setup environment as if they'd
			logged in
	echo
		prints the string specified (often used for scripts)
		echo * shows directory entries
	w	
	who
		These show various users online and some information about them
	id
		Specify the username and group id's the system
		sees you as currently.  Useful after su/sudo to determine
		what user you are for running/permissions
	last [name]
		Show the last logins/matched logouts/etc
		'last reboot' shows official reboots
	date
		Shows system date
	man <command>
		Show the help for the command, if available


Command usages
	stdin/stdout/stderr
		stdin is the pseudofile the text from a user or going
		"in" to a command.

		stdout is the data printed out from the command

		stderr is the data printed out from the command
		noted as 'error'
	args
		many arguments are '-<letter>' or '-<letter> <option>'
		Newer/gnu are often '--<text>' or '--<text> <option>'
		Sometimes options do not require the space
		many other options are files/text
	globs
		a form of search, often used for files
		Most common usage:
		* = zero or more of something
		? = exactly one of something
	pipes
		Stdout can be sent to the stdin of another command with '|'
		ie, 'cat /tmp/mymessage | mail ops@netops.mediaplex.com'
		will view the /tmp/mymessage file and send that to mail's
		stdin.  In this situation, that will use it for the message.
		Many executables treat stdin differently.  Some require
		the specification of '-' as the file, some default to
		stdin, and some wont pay any attention to stdin.

		Note that some data is stderr, not stdout
	redirects
		the stdout/stderr/stdin can be directed to/from a file.
		More advanced usage can be looked up or gone over specifically.
		The typical examples, however:

		> will attempt to start a new file (failing if the
		file exists or overwriting it, depending on the settings/
		system)
		ie: 'ls -R > /tmp/recursedirectory.txt'

		>> will attempt to append to an existing file (failing
		if the file doesnt exist or starting the file depending
		on the settings/system)
		ie: 'ls -l >> /tmp/recursedirectory.txt'
	
		For shell script, often '2>&1'
		2 = stderr, 1 = stdout.
		so it sends 2 (stderr) >& 1 (stdout).
		this keeps all the output in the same area.
		(particularily in crontabs)
	command concatenation
		command;command sequences commands after each other
	command aggregation
		() (like math)