Diff for "BashFAQ/066"

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

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

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

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

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
      ...
   fi

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

The regexp works as long as it is quoted with bash version 3.00.15(1)-release on CentOS4/RHEL4. I didn't bother checking whether bash is a patched version or not in CentOS4/RHEL4. --ellingsw