China DOS Union

So how do you tell what a handle points to?
echo 1&handle number to test is con
If con is displayed, then the handle value is con.
Otherwise it is nul or a file.

I didn't understand this part.

A typo correction:
echo 1&handle number to test is con
should be
echo 1<&handle number to test is con

It is equivalent to
echo is con 1<&handle number

Example analysis:
1<&7

means copying what handle 7 points to into handle 1.
And the output of echo is sent through handle 1 by default.
So if handle 7 points to con,
after copying it to 1, then 1 also points to con.
Then the output of echo will appear on the screen.
Otherwise it will not appear on the screen.

Of course, this is only a simple way to tell con from non-con.
For more specific methods, you'll still need to do more testing yourself.

[ Last edited by qzwqzw on 2009-6-13 at 21:14 ]

Originally posted by qzwqzw at 2009-6-13 09:11 PM:
A typo correction:
echo 1&handle number to test is con
should be
echo 1<&handle number to test is con

It is equivalent to
echo is con 1<&handle number

Example analysis:
1<&7

means ...

<& seems to be the same as >&, both copy the latter handle to the former handle.

Now I found that the only difference between >& and <&
is the default value on the left side.
The default left value of >& is 1.
The default left value of <& is 0.
The resulting effect is that after
echo. >nul 3>nul makes handle 1 become nul,
echo Hello Handle <&2 has no output
echo Hello Handle >&2 has output

Originally posted by qzwqzw at 2009-6-14 09:18 PM:
Now I found that the only difference between >& and <&
is the default value on the left side.
The default left value of >& is 1.
The default left value of <& is 0.
The resulting effect is that after
echo. >nul 3>nul ...

hh ntcmds.chm::/redirection.htm

If no handle is defined, the default handle for the < redirection input operator is 0, and the default handle for the > redirection output operator is 1.