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

[Florent Flament]

Frank Seifferth <seifferth@cl.uni-heidelberg.de> writes:

> 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.

I completely agree.

> 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'

Haha, nice catch.

> 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).

Indeed, this is beautiful.

Regards,
Florent