____________________________ Unix / Linux __________________________ 
You need to know about a dozen commands to function in any operating 
system.  Unix commands are short and mnemonic and very natural.
Most of them take various -flags to modify their action.  You can use
	alias newname "something"   to name "something" to "newname". 
e.g.	alias dir 'ls -lF'
All aliases and customizations may be placed in your ~/.tcshrc  file.
  ~/  refers to the home dir,   ./ to current dir,   ../  to parent dir
In general,   command -h   :shows the usage (syntax)
	      man command  :will tell you more than you want to know!

Here is a list of essential commands  [and useful aliases]:
  ls  = list   [ alias l 'ls -FC' ], [ alias d 'ls -lF \!* | more' ]
  cp  = copy            [ alias cp 'cp -ip' ]
  mv  = move, rename    [ alias r  'mv -i'  ]
  cd  = change dir
  rm  = remove (delete) [alias rm '/bin/rm -ir'],[ alias del /bin/rm ]
  vi  = visual editor (the standard Unix editor, see below)
  more  = display a file page-by-page
  mkdir = make dir
  rmdir = remove dir
  man   = manual (help) on a command
  chmod = change mode of file (set permissions)
  logout = log off the machine
  ssh   = log on to another machine (secure shell)
  scp   = (secure cp) copy files between machines 
There are hundreds of other commands/tools, do: xman  to see them.

_______________________________ vi editor______________________________ 
  vi filename   starts vi on the file, you'll be in command mode
  ZZ	write (save) and exit	 :q!  quit (exit) without saving
 h, j, k, l    move cursor left, down, up, right
  H	to top of page		 L	to bottom of page
  ^F	page forward		^B	page backward
  1G	to top of file		 G	to bottom of file
  i	insert        ...ESC	 a	append (after cursor)     ...ESC
  o	open new line ...ESC	 O	open new line above cursor...ESC
  x   delete character	 r   replace character  R ...ESC  replace 
  dw  delete word	 dd  delete line	D   delete to end-of-line
  Y :yank line(store in buffer)  3Y :yank 3 lines   4dd :delete 4 lines	
  p :put (write whatever is in buffer, below cursor)  P :put above cursor
  u :undo last change	 J :join lines(current with next)
There are many,many more commands and customizations, but these are the
most essential.  Current free incarnation is VIM, for linux, Win,...

_______________________________ zip/unzip______________________________ 
Best compress/archive utility.  zip -h , unzip -h  show the options.  
I use the following aliases:
  alias zp    'zip -oy'        # preserve date,skip links
  alias zpd   'zip -oymr'      # also -m: delete zipped files
  alias zpdr  'zip -oyr'       # also -r: recurse into subdir's
  alias zz    'unzip -l'       # list zipped files without extracting
  alias uz     unzip 	       # extract contents of zip-file

_______________________________ X Windows _____________________________ 
Each window is an xterm, emulating a terminal.  A window manager (such 
as gnome) manages all the windows and the mouse. Can be customized.  
The greatest thing about X is that you can run on a remote machine and 
display its output on your screen, immensely useful !!!

______________________________ Fortran / C ____________________________ 
gfortran code.f	 :compile Fortran code.f and produce executable a.out
  gcc    code.c	 :compile C       code.c and produce executable a.out

______________________________  Run a code ____________________________ 
The standard input/output device is the screen, unless redirected, e.g.
    a.out		will read and write to the screen, but
    a.out < dat      	will read from "dat" and write to screen
    a.out < dat > out	will read from "dat" and write to "out".

______________________________  Plotting  _____________________________ 
Simplest, nicest (and free) plotting tool ever is:  gnuplot
Start gnuplot with: gnuplot, then do: help plot ,  help set
Everything is on line, nothing to remember !!!   Try this:
   gnuplot> plot [-4:4] sin(pi*x), cos(pi*x/2) with lines | points
You can get a Windows version for your PC from 
 http://ftp.gnuplot.info/pub/gnuplot/