At the simplest, you could do:

my $result = qx{$ENV{ORACLE_HOME}/bin/sqlplus -L -V scott/scott \@data
+base 2>&1};
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You can read the documentation for qx/.../ in perlop. Probably a better solution would be to use Capture::Tiny:

use Capture::Tiny qw(capture);

my ($stdout, $stderr, $exit) = capture {
    system("$ENV{ORACLE_HOME}/bin/sqlplus", '-L', '-V', 'scott/scott',
+ '@database');
};
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Your original code escaped the @, so I carried that through in my examples. I'm not certain if that's intentional or not.