Generating Total Time in Milliseconds in SQL Developer - linux

Question

I need to replicate the linux command "date +%s%3N" in SQL Developer. I have tried the below code sample but it returns with a different value. I have also done extensive searching Google with no luck.
select to_char((extract(day from (systimestamp - timestamp '1970-01-01 00:00:00')) * 86400000
+ extract(hour from (systimestamp - timestamp '1970-01-01 00:00:00')) * 3600000
+ extract(minute from (systimestamp - timestamp '1970-01-01 00:00:00')) * 60000
+ extract(second from (systimestamp - timestamp '1970-01-01 00:00:00')) * 1000) * 1000) unix_time
from dual;
The date +%s%3N command returns something like:
1475615656692870653
Whereas the above code sample returns something like:
1475594089419116
The date command returns a longer and larger number than the code sample even though it was run before the code sample. The ultimate solution would be a direct utility in Oracle if possible. If not, possibly invoking the date command within Oracle would work.

Answer 1

Try this one:
CREATE OR REPLACE FUNCTION GetUnixTime RETURN INTEGER IS
dsInt INTERVAL DAY(9) TO SECOND;
res NUMBER;
BEGIN
dsInt := CURRENT_TIMESTAMP - TIMESTAMP '1970-01-01 00:00:00 UTC';
res:= EXTRACT(DAY FROM dsInt)*24*60*60
+ EXTRACT(HOUR FROM dsInt)*60*60
+ EXTRACT(MINUTE FROM dsInt)*60
+ EXTRACT(SECOND FROM dsInt);
RETURN ROUND(1000*res);
END GetUnixTime;
ROUND(1000*res) will return Unix time in Milliseconds, according to your question it is not clear whether you like to get Milliseconds, Microseconds or even Nanoseconds. But it is quite obvious how to change the result to desired value.
This function considers your local time zone and time zone of Unix epoch (which is always UTC)
If you don't like a function, you can write it at a query of course:
SELECT
ROUND(EXTRACT(DAY FROM CURRENT_TIMESTAMP - TIMESTAMP '1970-01-01 00:00:00 UTC')*24*60*60
+ EXTRACT(HOUR FROM CURRENT_TIMESTAMP - TIMESTAMP '1970-01-01 00:00:00 UTC')*60*60
+ EXTRACT(MINUTE FROM CURRENT_TIMESTAMP - TIMESTAMP '1970-01-01 00:00:00 UTC')*60
+ EXTRACT(SECOND FROM CURRENT_TIMESTAMP - TIMESTAMP '1970-01-01 00:00:00 UTC')
* 1000) AS unix_time
FROM dual;

Answer 2

I ended up going with using oscommands through the method described in this link here http://www.orafaq.com/scripts/plsql/oscmd.txt. The solutions below were a step in the right direction, however, other parts of the script we were making were running into issues. Using oscommands solved all of our issues. With the method mentioned in the link, I was simply able to type
l_time := oscomm('/bin/date +%s%3N');
to get the correct number.