Using a fixed filename can potentially cause problems if there are multiple processes, and a relative filename can cause problems if the user doesn't have write access in that directory. I'd recommend using File::Temp (a core module):

use File::Temp qw/tempfile/;

my ($tfh,$tfn) = tempfile(UNLINK=>1);
print $tfh <<'END_OF_SQL';
SET HEADING OFF;
SELECT systimestamp || ' IP=' || sys_context('USERENV','IP_ADDRESS') 
FROM dual;
EXIT
END_OF_SQL
close $tfh;

# the filename is in $tfn

# no "unlink" needed, that's automatic
[download]

I showed some more common File::Temp patterns that I use, such as creating the files in a specific directory, in this node. And because the above requires putting a variable into the external command being run, I'd recommend using a module to do that, such as e.g. capturex from IPC::System::Simple (see my node here).