# cat copies its input to stdout
<<<
foo
$$$ cat
>>>
foo

# or, given a bad flag, prints a platform-specific error and exits with non-zero status
$$$ cat --no-such-flag
>>>2 /(unrecognized|illegal) option/
>>>= !0

# echo ignores the input and prints a newline.
# We need the >>>= (or a >>>2) to delimit the whitespace which
# would otherwise be ignored.
$$$ echo
>>>

>>>2