Difference between Oracle 11g upgrade and 12c upgrade

While running main upgrade script there is a difference between 11g upgrade and 12c upgrade.

11g upgrade

$cd $ORACLE_HOME/rdbms/admin/

SQL> @catupgrd.sql

12c upgrade (not from SQL prompt)

$cd $ORACLE_HOME/rdbms/admin

$$ORACLE_HOME/perl/bin/perl catctl.pl catupgrd.sql

See also

Step by Step upgrade GI from 12.2 to 19.12 on AIX

Step by Step procedure for dry-run upgrade on RAC

CRS-6706: Oracle Clusterware Release patch on RAC