IF statement not working in RHEL 6 (workd in RHEL 5)

Question

I have a simple if statement that works fine in RHEL 5, but for some inexplicable reason, fails in RHEL 6:

if [[ ! $1 =~ "(one|two|three)" ]] ; then
    echo -e "\n***Invalid number"
    usage
    exit 1
else
    action=$1
fi  

I can use a case statement which works fine or re-write it but more than anything, I'm curious as to what has changed, assuming it is the version of RHEL and not something else?

Answer 1

regex must not not be quoted in newer BASH (starting from BASH version 3.2), try this:

if [[ ! "$1" =~ (one|two|three) ]] ; then
    echo -e "\n***Invalid number"
    usage
    exit 1
else
    action="$1"
fi 

To be able to use quoted regex you can use:

shopt -s compat31

EDIT: As glen commented below you can use !~ operator also i.e.

[[ "$1" !~ (one|two|three) ]]