How can I use a batch file to write to a text file?

You can use echo, and redirect the output to a text file (see notes below):

rem Saved in D:\Temp\WriteText.bat
@echo off
echo This is a test> test.txt
echo 123>> test.txt
echo 245.67>> test.txt

Output:

D:\Temp>WriteText

D:\Temp>type test.txt
This is a test
123
245.67

D:\Temp>

Notes:

• @echo off turns off printing of each command to the console
• Unless you give it a specific path name, redirection with > or >> will write to the current directory (the directory the code is being run in).
• The echo This is a test > test.txt uses one > to overwrite any file that already exists with new content.
• The remaining echo statements use two >> characters to append to the text file (add to), instead of overwriting it.
• The type test.txt simply types the file output to the command window.