Question

I try to use binary operator to use regexpression power,

   [[ wwwebhost@all =~ "^.+@.+$" ]]

do not work in bash 4.2 and works in bash 3.2

but this works in bash 4.2(drop the double quote):

   [[ wwwebhost@all =~ ^.+@.+$ ]]

can anyone explain this ?

Answer 1

In bash 4 (actually I thought this was added in 3.2, but maybe not) quotation marks on the right side of a =~ or == operator inside [[…]] tell bash to do simple string comparison rather than regular expression matching. You might think this would not be the case with the explicit “hey, do a regular expression match!” operator =~, but it is.