=~      Certain operations search or modify the string  "$_"
             by default.  This operator makes that kind of opera-
             tion work on some other string.  The right  argument
             is  a  search pattern, substitution, or translation.
             The  left  argument  is  what  is  supposed  to   be
             searched,  substituted, or translated instead of the
             default "$_".  The return value indicates  the  suc-
             cess of the operation.  (If the right argument is an
             expression other than a  search  pattern,  substitu-
             tion,  or translation, it is interpreted as a search
             pattern at run time.  This is less efficient than an
             explicit  search, since the pattern must be compiled
             every time the expression is evaluated.)   The  pre-
             cedence  of  this operator is lower than unary minus
             and autoincrement/decrement, but higher than  every-
             thing else.