Creating and Running .bat Files

Creating a batch file requires nothing more than a plain text editor -- Notepad, Notepad++, or VS Code all work fine. Type your commands one per line and save the file with a .bat extension, such as backup.bat. It's important to avoid word processors like Microsoft Word, which save rich text formatting (fonts, hidden markup) that cmd.exe cannot parse as valid commands; the file must be pure, unformatted text.

Once saved, you can run a batch file in two common ways: double-click it in File Explorer, or open cmd.exe and type its name (or full path) at the prompt. These aren't quite identical -- the current working directory when the script starts depends on how you launched it, and any command inside the script that references a relative path (like a subfolder or a file without a full path) resolves relative to that working directory, not necessarily the folder the script itself lives in.

Batch files can accept command-line arguments, which are available inside the script as %1 for the first argument, %2 for the second, and so on up through %9. This lets a single script behave differently depending on what's passed to it -- for example, greet.bat Alice would make %1 equal to Alice inside the script. There's also a useful built-in reference, %~f0, which always expands to the full path of the currently running script itself, handy for self-locating logic.

File encoding is a subtle but real gotcha. Batch files should be saved as plain ANSI text or UTF-8 without a byte-order-mark (BOM). Some editors, including older versions of Notepad, add an invisible BOM at the start of the file when you choose 'UTF-8' as the save format. That extra sequence of bytes can get prepended to your very first command, causing cmd.exe to fail to recognize it -- a confusing bug for anyone unaware the BOM is even there.