Current epoch time

Perl                    time

PHP                     time()

Java                  long epoch = System.currentTimeMillis()/1000;

MySQL                 SELECT unix_timestamp(now())

Oracle PL/SQL         SELECT (SYSDATE - TO_DATE('01-01-1970 00:00:00','DD-MM-YYY HH24:MI:SS')) * 24 * 60 * 60 FROM DUAL

JavaScript           Math.round(new Date().getTime()/1000.0) getTime() returns time in milliseconds.

Unix/Linux Shell     date +%s