Re: redirection to /dev/null

[Eli Schwartz]

On 9/9/20 8:16 PM, Koichi Murase wrote:
> 2020-09-10 8:04 Chris Elvidge <celvidge001@gmail.com>:
>> I've recently come across a crontab line:
>> 0 */6 * * *     /usr/bin/modprobed-db store &> /dev/null
> 
> `&>' is an extension to the POSIX shell, and the default setting of
> cron doesn't necessarily contain SHELL=/bin/bash.  For example, Ubuntu
> by default seems to use /bin/sh (dash) to run crontab.  If you want to
> use `&>' in crontab, you need to make it sure that "SHELL=/bin/bash"
> is set in the crontab.
> 
>> I've also read that '&> /dev/null' is outdated and should be replaced
>> with '>/dev/null 2>&1'
>>
>> True? And exactly why?
> 
> I'm also interested in whether it is really outdated and should not be
> used.
> 
> I can find some discussion on the first item on the page
> https://wiki.bash-hackers.org/scripting/obsolete .  The page says that
> it is because `&>' has a different unintended meaning in POSIX shell,
> but I think the discussion doesn't apply when one consciously writes
> Bash scripts (but not POSIX scripts).  If you cannot use any
> constructs that have a different meaning in the POSIX shell, you can
> never use arithmetic commands `((...))'  for example.
> 
> I don't know other sources of the recommendation.  AFAIK, the Bash
> manual doesn't mark it as deprecated nor obsolete.  Bash even added a
> new variant `&>>' in version 4.0, so I guess they are not considered
> outdated by the developer side.

The construct is identical in behavior to standard POSIX syntax, and
saves 4 bytes in the user's highly space-constrained file (lmao).

I don't avoid bash syntax which misbehaves in POSIX due to having
different meanings. But, personally, I would say not to use &> or &>>
due to it having no compelling advantage, but spreading the google cargo
cult of using it in #!/bin/sh scripts due to people never being taught
the difference. And it is a pointless context switch if you need to keep
track of one more thing you cannot use in #!/bin/sh scripts. Much easier
to always remember "the canonical way to redirect stdout/stderr in shell
scripts of all kinds, is >/dev/null 2>&1"

I have a similar objection to the use of "==" in [[ which IMHO is just
asking for trouble and leads to way too many scripts using [ == ] (which
bash also accepts, and I find more troubling than accepting the
pointless alias in [[ but I don't make the rules...)

-- 
Eli Schwartz
Arch Linux Bug Wrangler and Trusted User

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