ksh bug?

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# 8  
Originally Posted by MadeInGermany
Then let's call it a shortcoming.
It looks like -x mode uses stderr, and can conflict with redirection in the shell code.
It can get messy, yes.

This is also an issue for bash ...
$ bash -xc 'echo foo; exec 2>&1; echo bar' > stdout
+ echo foo
+ exec
$ cat stdout
+ echo bar

... but since it does not trace redirections, the destination of the trace won't change mid-command.

Originally Posted by MadeInGermany
Then, why stderr and not another file descriptor?
I would assume because stderr is known to be reserved for diagnostic and error messages, not data. If an alternative file descriptor were chosen, the possibility for a collision would still exist.

Corona688 makes an excellent point:
Originally Posted by Corona688
Being 'clever' about it would make obvious things, like redirecting a trace's output into a file, difficult.
Cleverness would include attempting to detect and handle a collision between the internal tracing descriptor and a script's redirections.


Last edited by alister; 11-21-2013 at 03:36 PM..
# 9  
Thank you Alister and Don!
I have been working on a script that captures failures from a "df".
Everything fine, until I wanted to quickly find a mistake in the post processing.
The difficulty was reason enough for me to change to #!/bin/bash
# 10  
As much as I like bash over ksh, I'm not sure that's a good reason. It uses stderr for trace output too.
# 11  
stderr=`df 2>&1 >/dev/null`
case $stderr in
*"Permission denied"*) ...
*"not a block device"*) ...;;

Any suggestions how to recode this?
# 12  
How about nohup?
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