I want to check if [[ $var == foo || $var == bar || $var == more ]] without repeating $var n times.

Here's a portable solution:

   case $var in
      foo|bar|more) ... ;;

And here's one that uses =~ (which requires bash 3.0 or higher):

   if [[ $var =~ $regex ]]; then

This one only works in bash 3.1 and some 3.2 revisions (it is untested in 3.0):

   if [[ $var =~ '^(foo|bar|more)$' ]]; then

The =~ operator behavior changes drastically between 3.1 and 3.2, so be careful with it. The above expression is tested to work in bash 3.1 and 3.2.{13,15,17}; and it doesn't work in 3.2.0. Please also note that the regexp does not need to be quoted in the 3.2 revisions where it works. --["redondos"]

Normally I would never advocate sticking code into a variable and attempting to use it -- lots of people have enormous trouble because they try to do that. In the case of =~, though, it seems to be required. Personally, I'd just stick with the case. --GreyCat