Separating sqlcmd's stdout and stderr - sqlcmd

Question

I need to implement a test harness for Azure SQL Data Warehouse using sqlcmd on Linux. In my test, I want to capture any error messages encountered by sqlcmd, but send the query results to /dev/null (using -o argument). In reviewing https://msdn.microsoft.com/en-us/library/ms162773.aspx, it seems that if -o is used, -r1 is meaningless.
-r[0 | 1]
Redirects the error message output to the screen (stderr). If you do not specify a parameter or if you specify 0, only error messages that have a severity level of 11 or higher are redirected. If you specify 1, all error message output including PRINT is redirected. Has no effect if you use -o. By default, messages are sent to stdout.
Having trouble understanding why stdout and stderr would be intermingled in this way.
Is my only recourse to run sqlcmd in the background while writing "stdout+stderr" to a named pipe and then strip off the error messages from the named pipe's results?
I don't want to incur any delay in writing the output, but do want to return the full results to the client.

Answer 1

Does "sqlcmd -i debug_dir/test2.sql -r1 2> /tmp/2.out 1> /tmp/1.out" work for you?
I tried it on my local box:
$> cat debug_dir/test2.sql
select * from test1;
go
select * from test1 where i = 'a';
go
select * from test2;
go
$> sqlcmd -S XXX -N -U YYY -P ZZZ -d AAA -I -i debug_dir/test2.sql -r1 2> /tmp/2.out 1> /tmp/1.out
$> cat /tmp/1.out
i j k
2 1 3
1 2 3
2 1 4
(3 rows affected)
a b c
2 1 4
11 12 4
11 12 3
2 1 3
$> cat /tmp/2.out
Msg 245, Level 16, State 1, Server XXX, Line 1
Conversion failed when converting the varchar value 'a' to data type int.
Msg 104309, Level 16, State 1, Server XXX, Line 1
There are no batches in the input script.
You can redirect to /dev/null instead of /tmp/1.out
I hope that helps.