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Church Of The
Swimming Elephant

Index | Description | Usage | Options | Variables | Hints | Bulletproof

Advanced Programming in Expect:
A Bulletproof Interface

Moving Window Diagnostics

Expect provides a means of controlling the output of its internal diagnostics and expression-matching attempts using the command "exp_internal".  The send_expect interface makes use of this command to create a diagnostics output file for each transmission attempt - for each attempt, a new diagnostics log file is created using exp_internal -f.  If transmission is successful, the file is deleted.  If it fails, the file is renamed using the syntax

n = the number of the failure
i = the spawn id of the channel that had the failure
command = the first word of the command string that failed to get sent properly. 
If you've ever read a 30 Megabyte log file with all of the diagnostics from the beginning to the end of execution, you'll understand why this is necessary.  The diagnostics files created using this method are usually less that 2 Kilobytes, and since they are directly associated with failures (because the window file is deleted for successful transmissions), debugging is far more efficient. At the end of execution, there should be at least as many diagnostic files as there were transmission errors; more if certain global flags are set.

Ideally, if there are no failures during execution, there should be no more than one send diagnostics file in existence at any time, named send.diagnostics.  If there are diagnostics files, each is associated with a particular failure and should be used in debugging that failure.


Setting Up The Interface
Using The send_expect Procedure
How It Works
Moving Window Snapshot Diagnostics
Controlling The Behavior Of The Interface
© 1999, dlf,


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