Date: Fri, 01 Nov 2013 11:36:22 -0500 From: Martin McCormick <martin@dc.cis.okstate.edu> Cc: "freebsd-questions@freebsd.org" <freebsd-questions@freebsd.org> Subject: Re: Inputs and outputs in the right order Message-ID: <201311011636.rA1GaMvq021035@x.it.okstate.edu>
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CyberLeo Kitsana writes: > In bourne-compatible shells (/bin/sh, bash) run 'set -x' or pass the -x > flag during invocation to turn on debug output. The shell will print out > each command it is about to invoke. > > The output requires some interpretation, as it can get confusing in the > presence of variable expansion, pipelines, and subshells; but it should > be adequate for a simple list of commands. Thanks for a great suggestion. This is a perl script which runs omshell commands to adjust the data base on a pair of DHCP servers. omshell has no echo facility or this whole exercise would have most likely just worked. As it is, it does a fine job of modifying the DHCP servers but the output is the sort that would confuse and frustrate folks who aren't used to seeing hex representations of IP addresses and outputs that repeat existing data plus add the newest change so it's better to evaluate the results of what just happened and tell the caller, "Added abc.okstate.edu to dh1" or "failed to remove abc.okstate.edu from dh1." That is easy to do in a script when you can corral all the pieces of the puzzle in one list or array. When everything works, we do actually get enough echoed information to do this but if someone is trying to delete a system that doesn't exist, we only end up with a notice of an object not found and no name or identifying information that a caller could use to know what wasn't found. The person suggesting the use of the $| variable in perl is on to the right idea if I can ever get a log file containing the commands to omshell plus omshells output after each command. As with all such problems, one learns a lot. I was unaware of $| in perl and how it disables buffering if set to anything other than 0. I will also ask the dhcp discussion group if anyone has tricked omshell in to echoing. You can't give it a flag to do so or tell it to echo. We are in the realm of tricks to essentially get something to do what it is not designed to do. Most of us tinkerers don't mind that to an extent, but I never sease to be amazed at what ordinary tasks just refuse to work at times. Thank you, all. Martin McCormick WB5AGZ Stillwater, OK Systems Engineer OSU Information Technology Department Telecommunications Services Group
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