Subj : Re: dosemu
To   : Al
From : tenser
Date : Wed Feb 05 2020 14:33:50

On 04 Feb 2020 at 04:14p, Al pondered and said...
 
 Al> I'm still not certain what I should do to eliminate the .bat file
 Al> displaying it's contents before the door runs, is 1>&2>/dev/null what I
 Al> want?

Short answer, I'm afraid I don't know why your batch file is displaying,
but that redirection is almost certainly NOT what you want.

My suspicion is that, if you opened up the .bat file itself, you'd see
it either directing itself to echo everything (I think that was a thing
in DOS batch files?  I honestly don't remember, and haven't touched MSFT
anything in many years.  I have some vague memory of `@echo on` or
something like that at the top of the file.  A quick search tells me that
prepending each command with '@' will disable echoing the command as the
batch file executes and that if you add `@echo off` as the first line of
the file it won't echo the commands it executes as it runs), or it's
explicitly cat'ing itself out (e.g. it has a line like `type me.bat`).

As for the redirection, let's consider what `1>&2>/dev/null` does.

First, let's break this into discrete tokens separated by whitespace
in order to consider them in more detail.  The shell will parse this
as:

    1>&2 > /dev/null

The first token means, "redirect file descriptor 1 to what file
descriptor 2 points to."  The _next_ two tokens (`>` and `/dev/null`)
mean, "redirect the standard output to the named file `/dev/null`.
But recall that the "standard output" is, by convention, file
descriptor 1.  Thus, what this means is, "redirect file descriptor
1 to /dev/null".  But recall that redirections happen _in order_,
from left to right.  So the sequence of events is, "redirect fd 1
to fd 2, and then redirect fd 1 to /dev/null."  The result, then,
is to simply redirect stdout to /dev/null; the first token is
essentially irrelevant as, even though it gets executed by the shell,
its effect is immediate undone by the next redirection.

Note that the syntax `1>&2` is a more explicit presentation of the
shorthand form, `>&2`.

It may be that you just want to redirect stderr, to prevent e.g.
error messages or the like from showing up.  In that case, ignore
stdout entirely, and just type something like: `foo 2>/dev/null`,
which just redirects fd 2 (which again, is conventionally the standard
error) to /dev/null.

Fun historical fact: the existence of `stderr` owes itself to the
invention of pipes in 3rd Edition Research Unix.  Before that, there
was no need for a separate error stream!

--- Mystic BBS v1.12 A44 2020/02/02 (Windows/32)
 * Origin: Agency BBS | Dunedin, New Zealand | agency.bbs.nz (21:1/101)

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