Re: redirection after braced block

[clemens fischer]

Matthew Woehlke wrote:

>>> clemens fischer writes:
>>>
>>>> I have the following construct in a script:
>>>>
>>>>   ... a number of commands
>>>>   {
>>>>       ... a number of commands
>>>>   } 2>&1 | ${prog_log} "${logfile}"
>>>>
>>>> It seems anything inside the braces is not seen by bash, and it
>>>> doesn't show up in a "sh -x ..." trace, but ${prog_log} does.  I
>>>> had debug echo's at the start of the block, they aren't triggered.
>
> This sort of construct seems to be working fine for me. Note that the
> contents of the block are executed in a subshell, and using 'true' as
> prog_log will suppress both stdout and stderr, as set up (though you
> might get a broken pipe error). So unless the commands in the block
> have side effects observable outside of the script, you won't know
> whether or not they execute.

Greg Wooledge observed in a private email that the parts of a pipeline
are executed in subshells.  Presumably he thinks that I set "prog_log"
in the feeder end rendering it without a defined value in the consumer,
but this variable is a global available to both.

But you made me see the light anyway!  Actually the logger was "system
${prog_log} "${logfile}"", with "system" being the customary

  system()
  {
      local cur_fun="${FUNCNAME[0]}"
      local ex=0
      msg "$*"
      [ ${opt_dryrun} -gt 0 ] && return 0
      type -t "${1}" >/dev/null 2>&1 && {
          eval "$@" || {
              ex=$?
              msg "$* exits ${ex}"
          }
      } || {
          msg "${1} undefined $?"
          ex=9999
      }
      return ${ex}
  }

and "msg" sending output to "1>&2".  As the script failed both with and
without that "system" prefix, I thought it didn't matter.  I thought the
commands in "system" are neutral to any data on stdin until the eval is
reached.

Now what I needed to have both normal and dry-run working is setting the
logger to "cat" and unsetting logfile for the latter case, then

    { ... } 2>&1 | ${prog_log} ${logfile+"${logfile}"}

does what I mean.  Does somebody know what's wrong with "system()" when
given data on stdin to be given to "eval"?


clemens