If I do the following in a batch file named test:
echo number=0 > file
and run it:
> test
> echo number=0 1> file
file contains:
number=0␣
If I change test to:
echo number=1> file
and run it:
> test
> echo number= 1>file
file contains:
number=
The 1 apparently is interpreted as stdout handle, which is comprehensible.
If I change test to:
echo number=0> file
– and 2 to 9 respectively – and run it:
> test
> echo number= 0>file
number=
the 0 and 2 to 9 apparently are interpreted as non-stdout handles and file is empty, which is comprehensible, too.
With:
echo "number=1"> file
file contains:
"number=1"
With:
echo (number=1)> file
file contains:
(number=1)
While writing the question I found the answer at How to avoid writing trailing spaces into text file on redirecting ECHO outputs to a file?:
Put the redirection in front of the command like:
> file echo number=0
or, as commented by Stephan, group the complete command, not just the argument:
(echo number=0) > file
(The title Using parenthesis/brackets to group expressions misses a bit, IMHO. It's to group commands and expressions, isn't it?)