diff

[Mark E. Fuller]

It's such a small thing, but I really enjoyed being privy to this 
question and discussion today.

On 14/12/2021 17:21, Daniel Shahaf wrote:
> אורי wrote on Tue, 14 Dec 2021 07:44 +00:00:
>> Actually I prefer the "<(..)" method, because sometimes I want to compare 2
>> commands:
>>
>> diff <(pip freeze | sort) <(cat requirements.txt | sort)
>>
> 
> Consider s/diff/comm -12/.
> 
>> Or even use cat and echo to add a specific line to one of the outputs. If I
>> want the result to be completely null. For example to run in crontab and
>> send me mail whether it's not null.
> 
> Careful here.  By default, cron jobs run not under your login shell but
> under /bin/sh, and it's possible the latter doesn't support «<(…)» even
> if the former does.

Out of curiosity I asked the internet: 
https://unix.stackexchange.com/questions/159513/what-are-the-shells-control-and-redirection-operators

Looks like < as a redirect is POSIX-compliant, but as soon as it's 
<(...) it's not a redirect anymore but instead a process substitution 
which is implemented in BASH, ZSH, etc.:
https://www.gnu.org/software/bash/manual/bash.html#Process-Substitution
https://zsh.sourceforge.io/Intro/intro_7.html

Nice to learn a new trick - I probably would have just redirected to a 
temp file instead of the compact solution discussed today.
> 
> Cheers,
> 
> Daniel
> 
> 
>> אורי
>> uri at speedy.net
>>
>>
>> On Tue, Dec 14, 2021 at 9:31 AM Eli Marmor <eli at netmask.it> wrote:
>>
>>> Use "-" instead the file name of one of both of the files, and pipe your
>>> output to the diff command.
>>>
>>> ‪On Tue, 14 Dec 2021 at 09:12, ‫אורי‬‎ <uri at speedy.net> wrote:‬
>>>
>>>> Thank you.
>>>>
>>>> אורי
>>>> uri at speedy.net
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>>>
>>
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Mark E. Fuller, Ph.D.
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