echo hello>test.txt
rem a single '>' will make a new file if one does not exist, and will overwrite
rem a previous file with the same line. to append to the same file, see below
echo hi>>test.txt
test.txt:
::hello
::hi
break >testfile.txt
@echo off
echo This is a test> test.txt
echo 123>> test.txt
echo 245.67>> test.txt
rem Or you can use variables:
set a=%RANDOM%
echo %a% > test.txt
(
echo Line1
echo Line2
...
echo Last Line
) > filename.txt