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Full Discussion: ksh bug?
Top Forums UNIX for Advanced & Expert Users ksh bug? Post 302876068 by alister on Thursday 21st of November 2013 02:22:26 PM
Old 11-21-2013
Quote:
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 ...
Code:
$ bash -xc 'echo foo; exec 2>&1; echo bar' > stdout
+ echo foo
+ exec
$ cat stdout
foo
+ echo bar
bar

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

Quote:
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:
Quote:
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.

Regards,
Alister

Last edited by alister; 11-21-2013 at 03:36 PM..
 

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SHELL-QUOTE(1p) 					User Contributed Perl Documentation					   SHELL-QUOTE(1p)

NAME
shell-quote - quote arguments for safe use, unmodified in a shell command SYNOPSIS
shell-quote [switch]... arg... DESCRIPTION
shell-quote lets you pass arbitrary strings through the shell so that they won't be changed by the shell. This lets you process commands or files with embedded white space or shell globbing characters safely. Here are a few examples. EXAMPLES
ssh preserving args When running a remote command with ssh, ssh doesn't preserve the separate arguments it receives. It just joins them with spaces and passes them to "$SHELL -c". This doesn't work as intended: ssh host touch 'hi there' # fails It creates 2 files, hi and there. Instead, do this: cmd=`shell-quote touch 'hi there'` ssh host "$cmd" This gives you just 1 file, hi there. process find output It's not ordinarily possible to process an arbitrary list of files output by find with a shell script. Anything you put in $IFS to split up the output could legitimately be in a file's name. Here's how you can do it using shell-quote: eval set -- `find -type f -print0 | xargs -0 shell-quote --` debug shell scripts shell-quote is better than echo for debugging shell scripts. debug() { [ -z "$debug" ] || shell-quote "debug:" "$@" } With echo you can't tell the difference between "debug 'foo bar'" and "debug foo bar", but with shell-quote you can. save a command for later shell-quote can be used to build up a shell command to run later. Say you want the user to be able to give you switches for a command you're going to run. If you don't want the switches to be re-evaluated by the shell (which is usually a good idea, else there are things the user can't pass through), you can do something like this: user_switches= while [ $# != 0 ] do case x$1 in x--pass-through) [ $# -gt 1 ] || die "need an argument for $1" user_switches="$user_switches "`shell-quote -- "$2"` shift;; # process other switches esac shift done # later eval "shell-quote some-command $user_switches my args" OPTIONS
--debug Turn debugging on. --help Show the usage message and die. --version Show the version number and exit. AVAILABILITY
The code is licensed under the GNU GPL. Check http://www.argon.org/~roderick/ or CPAN for updated versions. AUTHOR
Roderick Schertler <roderick@argon.org> perl v5.8.4 2005-05-03 SHELL-QUOTE(1p)
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