Re: Make ON_ERROR_STOP stop on shell script failure

On Fri, Mar 24, 2023 at 11:07 AM Peter Eisentraut <peter.eisentraut@enterprisedb.com> wrote:

On 20.03.23 19:31, Greg Stark wrote:
> So I took a look at this patch. The conflict is with 2fe3bdbd691
> committed by Peter Eisentraut which added error checks for pipes.
> Afaics the behaviour is now for pipe commands returning non-zero to
> cause an error*always*  regardless of the setting of ON_ERROR_STOP.

Commit b0d8f2d983cb25d1035fae1cd7de214dd67809b4 adds SHELL_ERROR as a set to 'true' whenever a \! or backtick command has a nonzero exit code. So it'll need some rebasing to remove the duplicated work.

So it's now possible to do this:

\set result = `some command`
\if :SHELL_ERROR
   -- maybe test SHELL_EXIT_CODE to see what kind of error
   \echo some command failed
   -- nah, just quit
   \q

\endif
 

> I'm not entirely sure that's sensible actually. If you write to a pipe
> that ends in grep and it happens to produce no matching rows you may
> actually be quite surprised when that causes your script to fail...

I agree that that would be quite surprising, and this feature would be a non-starter for them. But if we extended the SHELL_ERROR and SHELL_EXIT_CODE patch to handle output pipes (which maybe we should have done in the first place), the handling would look like this:

SELECT ... \g grep Frobozz
\if :SHELL_ERROR
  SELECT :SHELL_EXIT_CODE = 1 AS grep_found_nothing \gset
  \if :grep_found_nothing

  ...not-a-real-error handling...
  \else
  ...regular error handling...
  \endif
\endif

...and that would be the solution for people who wanted to do something more nuanced than ON_ERROR_STOP.