>perl -e "print qr(a\(bc)"
Unmatched ( in regex; marked by <-- HERE in m/a( <-- HERE bc/ at -e line 1.
>perl -e "print qr(a[(]bc)"
Search pattern not terminated at -e line 1.
>perl -e "print qr(a[\(]bc)"
(?-xism:a[(]bc)