Following the theme of Mike Galloy’s post yesterday, I’d like to show an example of noninteractive batch processing with IDL. The example below uses Linux and bash, though I used to do similar things on Solaris (and SunOS before that!) with tcsh, so it should work with slight modifications on other UNIX-based operating systems and command shells.
I’ll start with my canonical bash statement:
$ nohup nice $IDL_DIR/bin/idl < in.pro > out.txt 2> err.txt &
The first two commands are optional: nohup allows a process to continue even if you’ve started it on a remote server then disconnected from it, while nice decrements the priority of the process (to be “nice” to other users), thus preventing the process from grabbing all the CPU time on the machine. Because nohup and nice don’t recognize aliases, I directly call the IDL executive script in the bin/ directory of the IDL distribution. If you don’t use nohup and nice, you can invoke IDL with the standard “idl” alias instead. The character “<” redirects stdin, the contents of the file in.pro, to IDL; the character “>” redirects stdout to the file out.txt. Console and error messages are redirected with “2>” to err.txt. The ampersand “&” backgrounds the process, allowing interactive shell access.
Some detail is wrapped up in the file in.pro. It’s an IDL batch file, which consists of single IDL statements, no loops (though there is a trick to get around this). A batch file is not a program—it cannot be compiled. Rather, each statement in the file is interpreted and executed sequentially by IDL. Here’s in.pro:
print, 'Job started' n = 100 task1, n ;task2 ;task3 print, 'Job complete'
Note there is no END statement. The job of in.pro is to line up the tasks I want to execute; here, I’ve called them TASK1, TASK2, etc., each of which is an IDL program (I’ve chosen to use procedures to represent the tasks, but any program type will work). In this example, I’ll execute a single task:
pro task1, n compile_opt idl2 if n eq !null then n = 100 x = findgen(n) p = plot(x, /buffer, title='Plot #000') p.save, 'plot000.png', resolution=96 for i=1, n-1 do begin si = string(i, format='(i3.3)') p.title = 'Plot #' + si p.setdata, x + i p.save, 'plot' + si + '.png', resolution=96 endfor p.close end
TASK1 generates a series of N plots in an offscreen buffer, saving each plot, in turn, to a PNG file. It also serves as a simple example of batching with (New) Graphics—note the use of the SetData method to replace the plot data in each iteration.
After executing the bash statement above, here’s the contents of out.txt:
$ cat out.txt Job started Job complete
$ cat err.txt IDL Version 8.2.1 (linux x86_64 m64). (c) 2012, Exelis Visual Information Solutions, Inc. Trial version expires on 30-sep-2013. Licensed for personal use by ITTVISEvaluation Purposes Only only. All other use is strictly prohibited. % Compiled module: TASK1. % Loaded DLM: PNG.
and a (truncated) directory listing:
$ ls | head err.txt in.pro out.txt plot000.png plot001.png plot002.png plot003.png plot004.png plot005.png plot006.png
I’ve shown here a simple example of batch processing with IDL. Each step of the technique I’ve outlined above can have added complexity, which I hope to elaborate on in future posts. I hope you find this example useful, at least as a starting point.