Shell Programming and Scripting

Hi.
I am trying to help the OP solve his problem in an efficient way, so it makes sense to me to post the heart of his code with a correction that makes it work. If that can be done with a change of variable name, that seems easier than changing to the POSIX evaluation. He may still want to change to POSIX as his schedule allows, but most people need to get work done. The last part of the code is to show how using the string nan as a variable does not do what we might expect.
Same here for pdksh and bash, as well as zsh -- at least for all versions under which I ran the script s4.
As noted in the listing of OS and command versions in the output, that was done with ksh 93s+. As noted in post #9, the nan issue is present in 93s and 93t.

Best wishes ... cheers, drl

"ksh93 performs all calculations using the double precision floating point arithmetic type on your system." The New Kornshell Command and Programming Language by Bolsky and Korn.

So now you need to understand floating point arithmetic. If it's ieee floating point, +NaN, -NaN, +Inf, and -Inf must be supported. ksh93 has been stumbling on those constants, but the intent is to support ieee as fully as your system does.

NaN = not a number
Inf = infinity

In the ksh mailing list, they are always spelled NaN and Inf, I don't know if the all lower case spelling is considered to be acceptable. Some systems, and Cray comes very quickly to mind, do not support ieee floating point and cannot deal with NaN and Inf.

This is about all I know about nan and ksh93, so I can't shed much more light.

See this thread: https://mailman.research.att.com/pip...q4/001468.html