perldoc perlre

    In particular the following metacharacters have their
    standard egrep-ish meanings:

        \        Quote the next metacharacter
        ^        Match the beginning of the line
        .        Match any character (except newline)
        $        Match the end of the string
                 of the string)
        |        Alternation
        ()       Grouping
        []       Bracketed Character class