I want to check if [[ $var == foo || $var == bar || $var == more ]] without repeating $var n times.
The portable solution uses case:
# Bourne case "$var" in foo|bar|more) ... ;; esac
In Bash and ksh, Extended globs can also do this within a [[ command:
# bash/ksh -- ksh does not need the shopt shopt -s extglob if [[ $var = @(foo|bar|more) ]]; then ... fi