[gdavisson]

Brackets are used in shell wildcard ("glob") expressions. For example, if you try to use "[bar]" as a command, the shell will first look for files named "b", "a", and "r" in the current directory, and if it finds any it'll use the first one as the command name and any others as arguments to it.

But as far as I can see, using a close-bracket as the first character in a command is safe, since it cannot be treated as part of such a pattern. Open-bracket (without a matching close-bracket) would work in many shells, but will get you a "bad pattern" error in zsh.