[Trick] Preliminary streams redirection

[Dragokas]

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:: Preliminary streams redirection.
:: Published on 09.12.2012 by Alex Dragokas.
@echo off

:: All future streams #1, #2 will be redirerect to a file 'out.txt'
echo. 1>&3 2>&4 3>out.txt 4>&3

:: testing StdOut (descriptor #1)
Echo testing

:: imitation StdErr (descriptor #2)
copy zz:\

:: try StdIn
set /p "some=Your input: "

:: show message on console (without redirection)
pause>con

[Aacini]

viewtopic.php?f=3&t=2836&start=30

[dbenham]

Yes, that is a nasty CMD.EXE design flaw that was investigated thoroughly beginning at viewtopic.php?p=13436#p13436. The behavior was finally explained in two consecutive posts at viewtopic.php?p=14612#p14612.

The "trick" really should be avoided because it permanently locks the output file. The exclusive lock will not be released until the cmd session terminates. I suppose it could be useful in some specialized circumstances, but as a general rule, I don't like it.


Dave Benham

[Aacini]

Yes, that is a nasty CMD.EXE design flaw...

Dave Benham

Well, this is not exactly a nasty design flaw...


This behaviour is caused by the method that cmd.exe uses to achieve redirections, as explained in the last post of that thread. That method is the logical, most efficient one, from DOS internals point of view (BTW, file redirections in Unix-like operating systems are achieved in the same way).

In other words: if you would need to write an .exe program that internally manage file redirections, your program would use the same method and hence it would show the same behaviour under the same circumstances...

Antonio

[Dragokas]

Oh, thanks Aacini and dbenham.
I shall read that.
I'm surprise how many interestring researches you, experts, are maded all this time.
It's pity, I did not participated them.

So, I am also don't use this method.
Sometimes for a small scripts I prefer restarting like this:

Code: Select all

if "%~1"=="" (
  Echo Working...
  Call "%~dpnx0" 0 1>nul 2>&1
  Echo Ready...
  Goto :eof
)
:: main script

But with a file it also do an exclusive lock.
I use it in case where construction:

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(
icacls "%Cur%" /deny All:(DE,WDAC,WO,AS,WD,AD,WEA,DC,WA) /T /C
icacls "%Cur%" /grant All:(RC,S,GR,GW,GE,RD,REA,X,RA) /T /C
) 1>nul 2>&1

cause a critical error with closing a cmd:

/T was unexpected at this time.

Don't know why. Any ideas?