Re: Add SHELL_EXIT_CODE to psql

-- SHELL_EXIT_CODE is undefined
\echo :SHELL_EXIT_CODE
:SHELL_EXIT_CODE
-- bad \!
\! borp
sh: line 1: borp: command not found
\echo :SHELL_EXIT_CODE
127
-- bad backtick
\set var `borp`
sh: line 1: borp: command not found
\echo :SHELL_EXIT_CODE
127
-- good \!
\! true
\echo :SHELL_EXIT_CODE
0
-- play with exit codes
\! exit 4
\echo :SHELL_EXIT_CODE
4
\set var `exit 3`
\echo :SHELL_EXIT_CODE
3

Over in https://www.postgresql.org/message-id/eaf326ad693e74eba068f33a7f518039@oss.nttdata.com Justin Pryzby suggested that psql might need the ability to capture the shell exit code.

This is a POC patch that does that, but doesn't touch on the ON_ERROR_STOP stuff.

I've added some very rudimentary tests, but haven't touched the documentation, because I strongly suspect that someone will suggest a better name for the variable.

But basically, it works like this

-- SHELL_EXIT_CODE is undefined

\echo :SHELL_EXIT_CODE

:SHELL_EXIT_CODE

-- bad \!

\! borp

sh: line 1: borp: command not found

\echo :SHELL_EXIT_CODE

32512

-- bad backtick

\set var `borp`

sh: line 1: borp: command not found

\echo :SHELL_EXIT_CODE

127

-- good \!

\! true

\echo :SHELL_EXIT_CODE

0

-- play with exit codes

\! exit 4

\echo :SHELL_EXIT_CODE

1024

\set var `exit 3`

\echo :SHELL_EXIT_CODE

3

Feedback welcome.