On Mon, Aug 22, 2016 at 10:38 PM, <helmut.karlow...@ish.de> wrote: > When doing redirection inside a sub-process to a descriptor that is > redirected to a file the output of the subshell goes into the file. > > Now when the same descriptor is again redirected to another descriptor for > this whole > command-list, the output of the sub-process goes to the other descriptor. > > Except when the subshell is subject to process-substitution: In this > case the outer redirection has no effect to the sub-process. Why is that? > > Example: > > rm -f tb.err > exec 3>tb.err > echo ------ 1 ---------- > (echo 1 1>&3) 3>&1 > echo ........tb.err ........... > cat tb.err > echo ------ 2 --------- > echo >(echo 2 1>&3) 3>&1 > echo ........tb.err ........... > cat tb.err > echo ------ 3 --------- > echo >(echo 3 1>&3) > echo ........tb.err ........... > cat tb.err > > Only test 3 should print 3 into tb.err. bash and ksh93 also print > into tb.err in test 2, which is inconsistent compared to case 1. What's so > special about process-substitution regarding redirection? > > -Helmut >
Case 1 is totally different from the other two. 3>&1 redirects the fds for the coumpound command ( ) Case 2 is not really special, the redirection applies to the command (the first echo) not to its arguments in the same way echo $(echo 4 1>&3) 3>&1 prints in the file There is also another case that may be interesting: echo 3>&1 > >(echo 5 1>&3) in which 5 is not printed in the file, which makes sense to me as the process substitution is part of the redirections and not of the arguments.
