Shell Programming and Scripting

Okay, I've been working on a script for providing information on the progress of a backgrounded ditto command. Thanks to google and a lot of searching I've resolved all but one very odd error. At this point, I want to use xtrace (set -x) to try to uncover the issue. I have found several examples but none have quite helped me to acheive what I'm trying to do.

The idea is to be able to enable or disable xtrace via a script option (getopts), and capture the results in a file. What I've run into is that while I can create the file with no problem, all the debug info is displayed in the shell and not sent to the intended file. Is it possible to do this in this manner, or will I need to pass it from the command line?

Just in case it makes a difference, I am running OS X (10.5-10.7).

Thanks.

Code:

#!/bin/bash
while getopts "x" opt; do

	case $opt in
                x)     debugON=1;;
		\?) echo "Invalid option: -$OPTARG" >&2;;
	esac
done

if [ $debugON = 1 ]; then
     today=`date "+%m%d%Y"`
     set -x 2> ~/Desktop/xtrace$today
else
     set +x
fi

That will only redirect standard error for that one set statement and nothing else. If you want to redirect the standard error for the current execution environment you need to use exec.

Code:

exec 2>~/Desktop/xtrace$today
set -x

Note that all subsequenct commands will also inherit that as standard error. If that is undesirable, and you'd prefer for all commands other than the shell's tracing to continue to use the original stderr's destination, then you'll need to store it and override it per command (tedious and repetitious, but as far as I know the only way to do it).

Code:

exec 3>&2 2>~/Desktop/xtrace$today
set -x
date --bad-option 2>&3

You'd also need to store the original stderr if at some point you'd want to "undo" the tracing.

Code:

set +x
exec 2>&3 3>&-

Regards,
Alister

Perfect, that was exactly what I was looking for!