notes.txt

ls
-- list the contents of the directory

ls -l
-- list, long (the contents of the directory)
-- permissions: read/write/execute status
** -- drwxrwxrwx (directory, read, write, execute ... )
** -- drwx...... the user permissions (who created it)
** -- d...rwx... the group permissions
** -- d......rwx the public permissions
-- user setting
-- group setting
-- size
-- date
-- filename

ls -a
-- list, all (the contents of the directory)
-- shows hidden files (dot-files)

ls /etc
-- list, the contents of the etc directory

clear
-- clear the contents of the console

less filename.txt
-- opens a simple text editor like vi or nano.

more filename.txt
-- opens a simple text editor like vi, nano, or less.

cat filename.txt another_file.txt
-- displays the output of multiple files (as though they 
   were concatenated)... if you only list one file it 
   will concatenate it with nothing, and it's just used 
   to print out the files. If you don't save the output 
   to a new file, cat will not automatically save it for you. 

nano filename.txt
-- opens a simple text editor like vi, more, or less. 

mv oldname.txt newname.txt
-- move the file from one location (name) to another (name).
   This can be used to rename a file. 

mv oldname.txt directoryname/
-- move the file from the current directory to the new directory
   using the same name. This command will move oldname.txt from 
   the current directory to directoryname/oldname.txt

mv directoryname/oldname.txt .
-- move oldname.txt to the current directory ( . )

mv oldname.txt directoryname/newname.txt
-- move the file and rename it

mv old_dir/ new_dir/
-- move (rename) the directory from old_dir/ to new_dir/

cp oldfile.txt newfile.txt
-- copies the file from oldfile.txt to newfile.txt

cp old_dir/ new_dir/
-- NO... copy will not work on directories without the  
   recursive flag (see below)

cp -r old_dir/ new_dir/
-- copies a directory (and all the files within it) into a 
   new directory

rm filename.txt
-- remove (delete) the file, permanently

rm old_dir/
-- NO... remove will not work without the recursive flag

rm -r old_dir/
-- remove the directory (and all the files within it), permanently

mkdir new_dir/
-- makes a directory named new_dir

mkdir new_dir/sub_dir/subsub_dir/
-- NO... make directory won't make nested directories without the
   -p flag (paths? permissions?)

mkdir -p new_dir/sub_dir/subsub_dir/
-- make nested directories

whoami
-- print the name of the current user (probably displayed in the pompt)

sudo
-- superuser do, a method for running a command that requires permissions
   greater than the permissions assigned to the current user 

sudo adduser newusername
-- add a user to the system named newusername. It creates a user 'newusername'
   it also creates a group 'newusername' and it creates a new user 'newusername'
   with the group 'newusername.' It also creates a new directory for 'newusername'
   which is the home directory for this user. Creating a user also prompts us to
   enter information about the user: password, full name, room number, work phone
   home phone, and other.

su newusername
-- switch user to 'newusername.' It seems like it's kinda 'virtual' because if
   you exit from the switch user command you return to the user you were in before

exit
-- will pull you out a switch user (su) command. It will also log you out of an
   ssh connection. 

PERMISSIONS
-- r = read
-- w = write
-- x = execute
-- u = user level permissions
-- g = group level permission
-- o = other (world) level permission
-- drwx-rwx-rwx (d = it's a directory, no d = it's a file)
-- drwx-rwx-rwx (dir) (user) (group) (other)
-- if a permission is written it's true, if it's a dash it's false.

chmod [u/g/o][+/-][rwx] filename
-- change the mode (permissions) of the file
   Example: chmod o+w filename

Octal Permissions
-- r = 4
-- w = 2
-- x = 1
   rwx = 7
   rw- = 6
   r-x = 5
   r-- = 4
   -wx = 3
   -w- = 2
   --x = 1
   --- = 0

chmod [1-7/1-7/1-7] filename
-- change the mode (permissions) of the file using octal codes. The first set of
   octal codes is for the user. The second for the group. The third for other.

chown username filename
-- change the owner of the file. If you don't have the proper permissions you 
   may need run the command as a superuser (i.e. sudo chown username filename)

chown username:group filename
-- change the owner and the group of the file. You may need sudo. 

notes on the root user
-- root is all powerful, this user can override all permissions on every file
   and directory on the computer.

sudo
-- allows you to run a command as the root user, without explicitly switching
   to root or knowing the root password

!! 
-- run the last command I ran again (double bang)

sudo !!
-- append the last command to sudo, so that I don't have to retype everything
   if i realize I needed sudo  

top
-- a process manager that shows you real-time info about processes running 
   on the computer

ps
-- shows the processes that are running

ps aux
-- aux are options, usually they'd be passed with hyphens, but not here.
   aux will show all of the processes running on the computer, for all 
   the users 

ps aux | grep "top"
-- show all the processes and then pipe "|" the results to a grep search
   which looks for the pattern "top" and then only returns results that match

[Control-Z] (or Command-Z since I remapped it)
-- a shortcut for pausing a process and making it a job that I can start
   and stop when I want to move between programs

fg
-- foreground brings the (most recently used) job to the foreground 

fg [1-n]
-- bring job [number] to the foreground

jobs
-- list all the jobs running

[command] &
-- placing the ampersand "&" after a command will automatically move it to
   the background and place it in the jobs list. ... There seems to be an 
   error with getting my system to place the job in the background instead
   of stopping it. 

kill [PID]
kill -TERM [PID]
kill -SIGTERM [PID]
-- Kills the process that matches the process ID. By default it shuts down
   the process and allows it to exit gracefully (close files, etc.). Find
   the PID using "top" or "ps aux" or "ps aux | grep PROGRAMNAME"

kill -KILL [PID]
kill -SIGKILL [PID]
kill -9 [PID]
-- Kills the process that matches the process ID. Forces the process to
   quit. It seems like the force quit option in OSX's Activity Monitor

kill -STOP [PID]
-- Kills the process that matches the process ID and stops the job. It's
   similar to hitting Control-Z and pausing the process. 

env 
-- Print the environmental variables

$ENVNAME
-- The value of an environmental variable

ENVNAME="Value of the environmental variable"
-- Set/create the environmental variable with that value

echo
-- Echo back (print) the arguments that are passed to it. (e.g. echo $HOME)
   returns the value of the HOME variable

export ENVNAME="new value"
-- Set the environmental variable and save it to .bashrc (or .bash_profile)

export PATH=/new/path/to/bin:$PATH
-- Add a new dir path to the PATH variable, and then append the existing
   PATH variable by calling the variable ($PATH)