Below are a few basic, useful IDL commands:

• Reading in data

; it is necessary to declare the arrays first and then copy into them from a
; variable since IDL won't let you read from a file into an array directly
; this example is for an ASCII file, but you can read in binary, too
stuff = strarr(45) ; assumes 45 or fewer characters per line
newarr = fltarr(num lines in file); if you don't know num lines, you can open
nextarr = fltarr(num lines in file); the file and count the number of lines and close it
openr,unit no`um, "filename"
WHILE NOT EOF (unitnum)
        readf,unitnum, stuff
       newarr(counter) = strmid(stuff,0,10) ; the first ten chars are the first array
       nextarr(counter) = strmid(stuff,10,5); the rest of the line goes in this array
ENDWHILE
close, unitnum

• Plotting data. See the on-line help by typing in "?" or look in the IDL manual to get information on keywords

plot,x,y,keywords - for a linear-linear plot
plot_io, x, y, keywords - for a linear-log plot
plot_oo, x,y, keywords - for a log-log plot
surface, x,y,z, keywords - for a 3-D surface plot
contour, x,y, keywords - for a contour plot
tv, x,y,keywords - for an image display
image_cont - overlays a contour plot over a tv image
*note- the contour doesn't lay right over the image. 
       See my routine quickpic.pro for another way
       to do this

To plot more than one panel per page, type in:

!p.multi=[x,y,z] ; this is for num plots in x,y,and z

Then type in your plot commands. Remember to reset your values of [x,y,z] to [0,0,0]when you're done.

To display to a postscript file rather than to the screen, type in:

set_plot,'ps'
device,/landscape,filename='theanswer.ps'; for a landscape plot--portrait is the default

After issuing the desired display commands, type in:

device,/close

• Writing files

openw,unitnum, "filetofill"
printf,unitnum, variable
close,unitnum,"filetofill"

• Executing files
  A file is compiled each time you call it in IDL. To compile a file called fun.pro, type in:

IDL> .run fun

To execute the file, type in:

IDL> fun

Alternatively, you can create a make file that will automatically reset all your variables recompile everything. When you are editing several files at once, this is a handy way to go to avoid having to remember exactly where you've made changes since the last execution. Here's what the make.pro file looks like:

retall
.run main_driver
.run fun
.run sleep
.run dontDoThesis
.run neverGraduate

Then to compile everything and call the main driver, type in:

IDL> @make

IDL> main_driver

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Bidushi Bhattacharya
Dept of Atmos Sciences
UCLA
19 April 1998
bhattach@atmos.ucla.edu