Although one can easily make an executable file named
./42 or even
./カラオケ, I find no common packages that include letter-free commands. On Ubuntu, for example,
apt-file find . | grep -i -e '/[^a-z/_\-]+$' reports that every executable file's basename has at least a letter or underscore or dash. The only letter-free files or dirs that I found were non-executable, and usually version numbers:
Do any published rules or standards constrain how commands may be named? Or is this merely cultural practice?