Re: psql - better support pipe line

Heikki Linnakangas <hlinnaka(at)iki(dot)fi> writes:
> On 08/24/2015 08:06 AM, Pavel Stehule wrote:
>> it works perfectly - but the line
>> xargs -P 3 -I % sh -c "psql % -q -c 'analyze pg_attribute'; echo %"
>> is little bit ugly - with some psql option it can be cleaned to
>> xargs -P3 -I % psql % -q --echo-db -c "analyze pg_attribute" | ...
>> --echo-db requires -q option
>> What are you thinking about this idea?

> Seems like a one-tricky-pony to me. You're just as likely to need to
> print a relation name or something else, as the current database.

Not only that, but:

(1) there is no reason to believe that the db name and only the db name
is needed to do another connection; what about port, host, user, etc?

(2) this commandeers the pipe connection to transmit out-of-band data,
making it impossible to use the pipe for its natural function, viz
transmitting ordinary data from one processing step to the next. Sure,
there are use-cases where there's no such data and you can repurpose the
pipe like that, but that's an enormous limitation.

> Overall, once your pipeline gets that complicated, I'd rather write a
> little bash or perl script with for-loops and variables.

Yeah, on the whole this seems like a band-aid to let a bad scripting
approach limp a few steps further before it collapses completely.

regards, tom lane