Function execpline2 

pub fn execpline2(
    state: &mut estate,
    pcode: u32,
    how: i32,
    input: i32,
    output: i32,
    last1: i32,
)

Port of execpline2(Estate state, wordcode pcode, int how, int input, int output, int last1) from Src/exec.c:1989-2040. Recursive multi-stage pipe walker: at each step, analyse the current command, fork-into-pipe (if mid-pipeline) or exec directly (if WC_PIPE_END), then recurse on the next stage with pipes[0] as its input fd.