Practical Advice for Exercise 1

1) Some basic unix commands to know are
 
    mkdir [directory name] (make a directory)
    cd [directory name] (change directory)
    ls (list the files in a directory)
    cp [infile] [outfile] copy infile to outfile

2) At some point you may need to use a text editor.  You can't use
things like Word on unix text files!  Word files have all kinds of
hidden information, whereas text files store only the ascii characters.
GEDIT is probably the easiest approach.  To use it, just say

gedit [filename]

and a window will open with the contents of the file displayed.  You 
can simply type into that window, and then when you hit the Save button,
the contents of the window is saved to that filename.  There are a variety
of clever things you can do inside gedit, but the most basic is simply 
typing.  

3) You'll need to set up IRAF in your directory.  To do this, issue
the command "mkiraf" (for "make IRAF").  The "terminal type" should be
"xgterm" (for "X-graphics-terminal").  This should create a file
called "login.cl".  This login file contains a lot of choices of 
features that can be varied - you can read it and use it  but don't 
mess with it unless you know what you're doing.

4) To generate an xgterm window, type "xgterm &" in any kind of window -
then a new window should appear.  You should invoke IRAF in the new
window, by typing the command "cl" in that window.  This will work
properly only if you are in the directory where the "login.cl" file
is located.  The & at the end of any command will execute the command
in background mode and give you a prompt back, instead of just leaving
the window hanging.

5) When IRAF gets going, you'll see a prompt "cl>", and a list of 
IRAF subdirectories and commands (the subdirectories are the ones
with a "." at the end).  If you type a subdirectory name, you'll
get a list of additional commands/subdirectories that have been loaded,
and the prompt will change.  You can regenerate the list of commands
by typing "?".  You won't be needing these features for a while.

6) The four commands we'll be using for this exercise are
     imarith
     imcombine
     imstat
     imshift
We will go over these commands in class.

You can list the parameters of any command by typing "lpar [command]" 
(for "list parameters").  Those parameters that are listed at the top 
without parentheses are required each time you invoke the command - those 
with parens are not required, and you can often use the default values of 
these parameters.  If you want to change a parameter, you can do 
"epar [command]" which puts you into an editor (vi in my case - the
editor used is one of the things controlled by the login.cl file).
You can then edit the default values, and ":wq" out to get back to
the IRAF command line.  It's worth checking out the list of parameters
and their defaults just to see what's going on under the hood of these
commands.

7) "cd" and "ls" are IRAF commands that work just the same way they
do in unix.  You'll need to cd to the directory where the image files
are located to work on them.  If you want to issue other unix commands
from inside IRAF, you can do that by preceding the command with "!"
(e.g. "!vi [filename]" will activate the editor from within IRAF).

8) If you need more information on any IRAF command, you can do
"help [command]" within IRAF.  That'll tell you more than you would
ever want to know, including a precise description of all the input
parameters, and exactly what the command does.

9) Note that you can often abbreviate IRAF commands by the initial
letters - use "imcomb" instead of "imcombine" etc.  If you use too
few letters, it'll tell you that you've issued an ambiguous command.

10) Some useful features of IRAF include the "e" command, which gives
you back the previous command, or "e [com]" which gives you back the
most recent command that started "com" in this case.  Also, you can
use wildcards in the names of image files (that is "*.fits" means
all files that end ".fits").  * is the wildcard for any number of
characters, whereas ? is the wildcard for a single character.  Another
useful feature is the use of lists of images - if you make a textfile
that contains a list of image files (one image file per line), you can
use "@[filename]" instead of the whole list of images, where [filename]
is the name of the file containing the list of images.  This is very
useful, esp in conjunction with the IRAF "files" command, which you
can explore for yourself.

11) Dealing with the difference between the backspace and delete keys
is a pain - it works differently within IRAF than it does from most
UNIX systems.