Expansions are a great tool in bash and there are a lot of applications as well as expantion types, from bash documentaion: Expansion is performed on the command line after it has been split into tokens. There are seven kinds of expansion performed: brace expansion tilde expansion parameter and variable expansion command substitution arithmetic expansion word splitting filename expantion The order of expansions is: brace expansion; tilde expansion, parameter and variable expansion, arithmetic expansion, and command substitution (done in a left-to-right fashion); word splitting; and filename expansion.