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Re: bug#51311: [PATCH] echo: update --help to document edge cases
From: |
Florent Flament |
Subject: |
Re: bug#51311: [PATCH] echo: update --help to document edge cases |
Date: |
Thu, 21 Oct 2021 19:43:18 +0200 |
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