Function posix_flat_rewrite 

pub fn posix_flat_rewrite(command: &str, cmds: &[FlatCmd]) -> String

The ungrouped form for bash and zsh: each marked command gets its own pipe, and pipefail makes each pipe exit with the command’s status, so && and || behave as before and builtins run in the shell itself. The shell must not keep state between commands, or pipefail leaks.