assignment of the result of a subprocess to a variable hangs

[areman]

> ver
Microsoft Windows [Version 10.0.15063]

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 16.04.2 LTS
Release:        16.04
Codename:       xenial

I installed the oracle instant client

sudo apt-get install -y alien
alien -i oracle-instantclient12.2-basic-12.2.0.1.0-1.x86_64.rpm 
alien -i oracle-instantclient12.2-sqlplus-12.2.0.1.0-1.x86_64.rpm

sqlplus itself works fine. I can connet to databases without any problem.

But when I try to assign the result of a sqlplus command to a variable the bash hangs.

value=$( sqlplus -s user/password@DB <<SQL
select 1 from dual;
exit;
SQL
)

The sqlplus call itself finished successful and the subshell finished. But something hangs and the calling bash doesn't get the "focus" back.

Without a variable assignment it works.

( sqlplus -s user/password@DB <<SQL
select 1 from dual;
exit;
SQL
)

It seems the problem has something to do with the output streams. Add a simple pipe and it works.

echo $( sqlplus -s user/password@DB <<SQL 2>&1 | cat
select 1 from dual;
SQL
)

[ethanherbertson]

I see something very similar happening in Perl.

Doing something like

my $output = `sqlplus -S /nolog \@define.sql`;

causes a "hang", where the statement never finishes executing. However, doing something like

exec `sqlplus -S /nolog \@define.sql`;

behaves correctly.

If I do a "streaming" version of the same thing, I can confirm that the sqlplus command itself does in fact complete:

open my $cmd_fh, '-|', 'sqlplus -S /nolog @define.sql 2>&1 && echo \'done\'';
print "Line: $_" while (<$cmd_fh>);
close $cmd_fh;

prints:

→ perl thing.pl
Line: DEFINE _SQLPLUS_RELEASE = "1202000100" (CHAR)
Line: done

And then hangs.

[therealkenc]

Not sure how this one got lost in the noise and wasn't marked need-repro from the get-go. If you are experiencing the problem in 1809 (aka 17763 aka RS5 aka October 2018 update) you can try rebooting the issue following CONTRIBUTING.md with particular attention to pasteable CLI repro steps from clean install and an strace log.

[ethanherbertson]

Not sure how this one got lost in the noise and wasn't marked need-repro from the get-go. If you are experiencing the problem in 1809 (aka 17763 aka RS5 aka October 2018 update) you can try rebooting the issue following CONTRIBUTING.md with particular attention to pasteable CLI repro steps from clean install and an strace log.

I can't get away with clean-slating my current setup, but I'll see what I can do.

[therealkenc]

You can generally fake it; what's important is the repro and the strace, noting that the probability of the issue getting attention is inversely proportional to the number of steps. How "clean" is relative. Another alternative is to install 16.04 from the Store (if you are running 18.04) or vice-verse. The Ubuntu version isn't going to make a difference, given the OP was from last year. [ed Notwithstanding any repro to go on I think this might be #2786 related so trying the October 2018 Update will matter.] Bonne chance.