Each single-line input can be derived from line:
line ::= group "\n"
group ::= cmd ( sp ord_pipe )* [ sp num_pipe [ group ] | sp fredir ]
ord_pipe ::= "|" sp cmd
num_pipe ::= ( "|" | "!" ) num
fredir ::= ">" sp file
cmd ::= file ( sp arg )*
arg ::= word
file ::= word
sp ::= " "+
num ::= ( "0"..."9" )+
word ::= ( num | "a"..."z" | "A"..."Z" | "." | "-" | ":" | "\\ " )+