On 12/03/2010 07:46 AM, Payam Poursaied wrote: > > Hi all, > I'm not sure this is a bug or please let me know the concept: > What is the difference between: > ls -R /etc/ 2>&1 1>/dev/null > and > ls -R /etc/ 1>/dev/null 2>&1
POSIX requires that redirections are evaluated from left to right. The first line duplicates fd 2 from 1 (that is, stderr is now shared with stdout), then changes fd 1 onto /dev/null (so you've silenced stdout, and errors from ls will show up on your stderr). The second line changes fd 1 onto /dev/null, then duplicates fd 2 from 1 (that is, stderr is now shared with /dev/null, and you've silenced all output to either stream). > the second one redirect everything to /dev/null but the first one, still > prints errors (run as a non root user would unveil the problem) > it the order of arguments important? If yes, what is the idea/concept behind > this behavior? Yes the order is important, and the idea behind the behavior is that left-to-right evaluation order can be easily documented and relied on. -- Eric Blake ebl...@redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org
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