Re: bug#51311: [PATCH] echo: update --help to document edge cases

[Frank Seifferth]

On Thu, 21 Oct 2021 08:46:17 -0600 Glenn Golden <gdg@zplane.com> wrote:
> -----------------------------------------------------------------------------
> NOTE
>   For historical and back-compatibility reasons, certain bare option-like
>   strings cannot be emitted without setting POSIXLY_CORRECT, and the bare
>   string '-n' cannot be emitted at all.  Prefixing or suffixing such strings
>   with quoted whitespace (e.g. ' -n') can be used as a workaround for this
>   peculiarity.  More generally, printf(1) is recommended as a more modern
>   and flexible replacement for tasks historically performed by echo(1).
> -----------------------------------------------------------------------------
> 
> Something like this seems to get the job done: Briefly states the issue,
> why it exists, provides a workaround, and cheerleads for modernization. 

This note does seem to be in order and it will certainly benefit everyone
who may read the manpage. It is not entirely accurate, however. `echo`,
when run with the `-e` option, does allow backslash escapes for arbitrary
octal and hexadecimal representations of character codes. Hence both of
the following commands will produce the string `-n` as output:

    echo -e '\0055n'
    echo -e '\x2dn'

For the sake of correctness, one might want to reword the note somewhat
like this:

  For historical and back-compatibility reasons, certain bare option-like
  strings cannot be passed to echo as non-option arguments. The only way
  to echo the string '-n', for instance, is to specify the dash in either
  octal or hexadecimal representation (e.g. 'echo -e "\x2dn"'). It is
  therefore not advisable to use echo(1) for printing unknown or variable
  arguments. More generally, printf(1) is recommended as a more modern
  and flexible replacement for tasks historically performed by echo(1).


Regards

Frank