BNF

list ::= pipeline | list '&&' pipeline | list '||' pipeline

pipeline ::= command | pipeline '|' command

command ::= simple_command | '(' list ')' redirect_list

simple_command ::= WORD | redirect_list simple_command | simple_command cmd_suffix

cmd_suffix ::= io_redirect | WORD | cmd_suffix io_redirect | cmd_suffix WORD

redirect_list ::= io_redirect | redirect_list io_redirect

io_redirect ::= io_file | io_here

io_file ::= '<' WORD | '>' WORD | '>>' WORD

io_here ::= '<<' WORD