Function tee 

pub async fn tee(ctx: CommandContext) -> CommandResult

Execute the tee command

Reads stdin, copies it to stdout so the pipeline keeps flowing, and writes the same bytes to every file operand. File operands are truncated unless -a is given. A file that cannot be written reports an error and sets the exit code to 1, but the remaining files and stdout are still written, which is what GNU tee does.