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Full Discussion: can't close stdin/stdout in shell
Top Forums Shell Programming and Scripting can't close stdin/stdout in shell Post 302396446 by Corona688 on Thursday 18th of February 2010 12:29:22 PM
Old 02-18-2010
Quote:
Originally Posted by mandelbrot333
ls -l /proc/self/fd >&2
You are redirecting stdout (what ls is producing) into stderr (&2).
Quite so. I have also already redirected /dev/null into stdin, and stdout into /dev/null.
Quote:
Unless you tell the script to dump stderr to /dev/null...:
Code:
./myscript 2>/dev/null

I don't want to redirect stderr, and have already redirected stdin and stdout to /dev/null. I expected ls to inherit stdin and stdout from the shell, but instead the shell for some copies stderr into stdout -- but only when I redirect ls's stdout. It doesn't just do this for terminals, either -- I've seen it do so for files, so I boiled the problem down to its minimum representation here.
Quote:
...it will be output to the shell you are running the script in.
Which is /dev/null, of course, given the prior redirections. But when I redirect it into stderr, the shell takes the extraordinary step of restoring stdout to its previous state.
Last edited by Corona688; 02-18-2010 at 01:34 PM..
 

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LEARN ABOUT REDHAT

smrsh

SMRSH(8)						      System Manager's Manual							  SMRSH(8)

NAME

       smrsh - restricted shell for sendmail

SYNOPSIS

       smrsh -c command

DESCRIPTION

       The smrsh program is intended as a replacement for sh for use in the ``prog'' mailer in sendmail(8) configuration files.  It sharply limits
       the commands that can be run using the ``|program'' syntax of sendmail in order to improve the over all security of your system.   Briefly,
       even  if  a  ``bad guy'' can get sendmail to run a program without going through an alias or forward file, smrsh limits the set of programs
       that he or she can execute.

       Briefly, smrsh limits programs to be in a single directory, by default /etc/smrsh, allowing the system administrator to choose the  set	of
       acceptable  commands, and to the shell builtin commands ``exec'', ``exit'', and ``echo''.  It also rejects any commands with the characters
       ``', `<', `>', `;', `$', `(', `)', `
' (carriage return), or `
' (newline) on the command line to prevent ``end run'' attacks.  It allows
       ``||'' and ``&&'' to enable commands like: ``"|exec /usr/local/bin/procmail -f- /etc/procmailrcs/user || exit 75"''

       Initial	pathnames  on programs are stripped, so forwarding to ``/usr/ucb/vacation'', ``/usr/bin/vacation'', ``/home/server/mydir/bin/vaca-
       tion'', and ``vacation'' all actually forward to ``/etc/smrsh/vacation''.

       System administrators should be conservative about populating the /etc/smrsh directory.	Reasonable additions are vacation(1), procmail(1),
       and  the  like.	 No  matter  how brow-beaten you may be, never include any shell or shell-like program (such as perl(1)) in the /etc/smrsh
       directory.  Note that this does not restrict the use of shell or perl scripts in the sm.bin directory (using the ``#!'' syntax); it  simply
       disallows execution of arbitrary programs.

FILES

       /etc/smrsh - directory for restricted programs

SEE ALSO

       sendmail(8)

							   $Date: 2002/04/25 13:33:40 $ 						  SMRSH(8)
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