how to display full stored procedure code?

Question

\df+ <function_name> in psql.

\ef <function_name> in psql. It will give the whole function with editable text.

SELECT prosrc FROM pg_proc WHERE proname = 'function_name';

This tells the function handler how to invoke the function. It might be the actual source code of the function for interpreted languages, a link symbol, a file name, or just about anything else, depending on the implementation language/call convention

use pgAdmin or use pg_proc to get the source of your stored procedures. pgAdmin does the same.

Use \df to list all the stored procedure in Postgres.

If anyone wonders how to quickly query catalog tables and make use of the pg_get_functiondef() function here's the sample query:

SELECT n.nspname AS schema
      ,proname AS fname
      ,proargnames AS args
      ,t.typname AS return_type
      ,d.description
      ,pg_get_functiondef(p.oid) as definition
--      ,CASE WHEN NOT p.proisagg THEN pg_get_functiondef(p.oid)
--            ELSE 'pg_get_functiondef() can''t be used with aggregate functions'
--       END as definition
  FROM pg_proc p
  JOIN pg_type t
    ON p.prorettype = t.oid
  LEFT OUTER
  JOIN pg_description d
    ON p.oid = d.objoid
  LEFT OUTER
  JOIN pg_namespace n
    ON n.oid = p.pronamespace
 WHERE NOT p.proisagg
   AND n.nspname~'<$SCHEMA_NAME_PATTERN>'
   AND proname~'<$FUNCTION_NAME_PATTERN>'