In Sybase Adaptive Server Enterprise (Sybase ASE) you can use STR_REPLACE function to replace all occurrences of a substring in string. In PostgreSQL you can use REPLACE function.
Sybase ASE:
-- Replace 'bc' with '12' SELECT STR_REPLACE('abcd', 'bc', '12'); # a12d
PostgreSQL:
-- Replace 'bc' with '12' SELECT REPLACE('abcd', 'bc', '12'); # a12d
For more information, see Sybase ASE to PostgreSQL Migration.