bnf

OPE_AND		= &&
OPE_OR		= ||
OPE_PIPE	= |
OPE_LEFT	= [< | <<]
OPE_RIGHT	= [> | >>]
OPE_SEMI	= ;
OPE_REDIR	= [OPE_LEFT | OPE_RIGHT]
OPE_ALL		= [OPE_AND | OPE_OR | OPE_PIPE | OPE_REDIR]
WORD		= !OPE_ALL

exp 			::= or_exp [OPE_SEMI exp]?
or_exp			::= and_exp [OPE_OR or_exp]?
and_exp			::= pipe_exp [OPE_AND and_exp]?
pipe_exp		::= redir_exp [OPE_PIPE pipe_exp]?
redir_exp		::= redir_standard_left | redir_special_left
redir_standard_left	::= redir_right [OPE_LEFT redir_exp]?
redir_special_left	::= OPE_LEFT file redir_exp
redir_right		::= redir_standard_right | redir_special_right
redir_standard_right	::= command [OPE_RIGHT file]?
redir_special_right	::= OPE_RIGHT file command

command			::= cmd [args]*

cmd			::= WORD
args			::= WORD
file			::= WORD