DosTips.com

Code: Select all

@echo off
0<test.txt 7>test.txt 8<&0 9<test.txt (
  call :read 0
  call :write 1
  call :write 2
  call :write 3
  call :read 0
  call :read 8
  call :read 9
  call :write 4
  call :read 8
  call :read 8
  call :read 0
  echo(
  echo FINDSTR from 9 does not reset file pointer to beginning, and ends at EOF:
  0<&9 findstr "^"
  echo(
  call :read 9
  0<test.txt (
    echo(
    echo Temporarily reopen input file via 0
    call :read 0
    call :read 0
    echo Close and resume old 0
    echo(
  )
  call :write 5
  call :read 0
  call :read 9
  call :read 0
  call :read 8
  call :read 9
  echo(
  echo FINDSTR from 0 does not start at beginning:
  findstr "^"
  echo(
  echo FIND from 0 resets file pointer to beginning, and ends at EOF:
  find /v ""
  echo(
  call :read 0
  echo(
  echo Cannot reopen output file because of exclusive lock
  1>test.txt (
    1>&2 echo This is never executed
  )
  echo(
  echo Cannot read from non-existent file
  0<notExists (
    set /p "ln=This is never executed"
  )
  echo(
  1>&0 (
    1>&2 echo Cannot write to input handle, but redirection worked and error message puzzling
    echo This fails when try to write to input handle
  )
  echo(
  0<&1 set /p "ln=Why does read from output handle not generate an error message?"
  echo(
)
exit /b


:read  handle
setlocal
if "%1" neq "0" set "src=0<&%1"
set "ln="
set /p "ln=" %src%
echo Reading from %1 ==^> %ln%
exit /b

:write  txt
1>&7 echo %*
echo Wrote %*
exit /b

Code: Select all

Reading from 0 ==>
Wrote 1
Wrote 2
Wrote 3
Reading from 0 ==> 1
Reading from 8 ==> 2
Reading from 9 ==> 1
Wrote 4
Reading from 8 ==> 3
Reading from 8 ==> 4
Reading from 0 ==>

FINDSTR from 9 does not reset file pointer to beginning, and ends at EOF:
2
3
4

Reading from 9 ==>

Temporarily reopen input file via 0
Reading from 0 ==> 1
Reading from 0 ==> 2
Close and resume old 0

Wrote 5
Reading from 0 ==> 5
Reading from 9 ==> 5
Reading from 0 ==>
Reading from 8 ==>
Reading from 9 ==>

FINDSTR from 0 does not start at beginning:

FIND from 0 resets file pointer to beginning, and ends at EOF:
1
2
3
4
5

Reading from 0 ==>

Cannot reopen output file because of exclusive lock
The process cannot access the file because it is being used by another process.

Cannot read from non-existent file
The system cannot find the file specified.

Cannot write to input handle, but redirection worked and error message puzzling
The system cannot find the file specified.

Why does read from output handle not generate an error message?

Code: Select all

@echo off &setlocal enableDelayedExpansion

echo.
echo.test0
(set/A=)3>&2>&1>nul&&echo.yes||echo.no

echo.
echo.test1
(set/A=)3>nul 2>nul >nul&&echo.yes||echo.no

echo.
echo.test2
(((set/A=)3>&2)2>&1)>nul&&echo.yes||echo.no

echo.
echo.test3
(set/A=)1>&2 2>&3 3>nul&&echo.yes||echo.no

pause
exit

Code: Select all

test0
Er ontbreekt een operand.
no

test1
no

test2
no

test3
Er ontbreekt een operand.

Code: Select all

handle   before   after
     0   STDIN    STDIN
     1   STDOUT   nul
     2   STDERR   STDERR
     3   unused   STDOUT
    4+   unused   unused

Code: Select all

Z:\>test.bat

test0
Fehlender Operand
no

test1
no

test2
no

test3
Fehlender Operand
>&3 cmd
Microsoft Windows [Version 6.3.9600]
(c) 2013 Microsoft Corporation. Alle Rechte vorbehalten.

Z:\>

Code: Select all

(((set/A=)3>&2)2>&1)>nul&&echo.yes||echo.no
(((set/A=)3>nul)2>nul)>nul&&echo.yes||echo.no
:: ...

Code: Select all

0>&1 echo TEST 3>con

Code: Select all

handle mapping   handle    initial   assign             restore
                                     0>&1     3>con     0        3
                      0    STDIN     STDOUT   STDOUT    CON      CON
                      1    STDOUT    STDOUT   STDOUT    STDOUT   STDOUT
                      2    STDERR    STDERR   STDERR    STDERR   STDERR
                      3    unused    STDIN    CON       unused   STDIN
                      4    unused    unused   STDIN     STDIN    unused
                     5+    unused    unused   unused    unused   unused
restore handle             -         0        0,3       3        -
        with               -         3        3,4       4        -

Code: Select all

String input;
boolean echoEnabled = true;
while (true) do {
   if (echoEnabled) streamFromHandle(1).write(getPrompt());
   input = streamFromHandle(0).readLine();
   execute(input);
}

Code: Select all

C:\test>3<&1 <h:test.txt (<&3 pause&set /p val=First time I leave the thumb drive plugged in)
Press any key to continue . . .
First time I leave the thumb drive plugged in
C:\test>echo %errorlevel%
0

C:\test>set val
val=ok

C:\test>set "val="

C:\test>3<&1 <h:test.txt (<&3 pause&set /p val=Now I remove the thumb drive before pressing a key)
Press any key to continue . . .
Now I remove the thumb drive before pressing a key
C:\test>echo %errorlevel%
1

C:\test>set val
Environment variable val not defined

C:\test>

Code: Select all

C:\test>>h:test.txt (echo I remove the thumb drive while pausing&pause >&2&echo This failed ECHO does not set a detectable error code||>&2echo FAILURE!)
Press any key to continue . . .
The system cannot find the file specified.

C:\test>ECHO %errorlevel%
0

Code: Select all

2>nul set/a=&&echo.yes||echo.no