sh

One SH file of 61 bytes. A shell script is the Linux and macOS counterpart of a batch file, and one saved with the executable permission can run with a single command. This one starts with a shebang line and prints a short harmless message. Use it to check that your upload form rejects .sh, that the check is not case sensitive, and that the stored copy, if it is kept, does not get executable permissions. Also verify that downloading it back serves it as a plain attachment and does not display or run it in the browser.