How to display the function, procedure, triggers source code in postgresql?

\sf function_name in psql yields editable source code of a single function.

From https://www.postgresql.org/docs/9.6/static/app-psql.html:

\sf[+] function_description This command fetches and shows the definition of the named function, in the form of a CREATE OR REPLACE FUNCTION command.

If + is appended to the command name, then the output lines are numbered, with the first line of the function body being line 1.

Since Version: psql (9.6.17, server 11.6)

I have tried all of above answer but For me

postgres=> \sf jsonb_extract_path_text
CREATE OR REPLACE FUNCTION pg_catalog.jsonb_extract_path_text(from_json jsonb, VARIADIC path_elems text[])
 RETURNS text
 LANGUAGE internal
 IMMUTABLE PARALLEL SAFE STRICT
AS $function$jsonb_extract_path_text$function$



postgres=> \df+
ERROR:  column p.proisagg does not exist
LINE 6:   WHEN p.proisagg THEN 'agg'
               ^
HINT:  Perhaps you meant to reference the column "p.prolang".

df seems not working for me.

To list all functions:

select n.nspname as function_schema,
       p.proname as function_name,
       l.lanname as function_language,
       case when l.lanname = 'internal' then p.prosrc
            else pg_get_functiondef(p.oid)
            end as definition,
       pg_get_function_arguments(p.oid) as function_arguments,
       t.typname as return_type
from pg_proc p
left join pg_namespace n on p.pronamespace = n.oid
left join pg_language l on p.prolang = l.oid
left join pg_type t on t.oid = p.prorettype 
where n.nspname not in ('pg_catalog', 'information_schema')
order by function_schema,
             function_name;

Now if you want to search a specific word or text in all function is something like that, make sure you replace your text in the function:

with tbl as (
select n.nspname as function_schema,
       p.proname as function_name,
       l.lanname as function_language,
       case when l.lanname = 'internal' then p.prosrc
            else pg_get_functiondef(p.oid)
            end as definition,
       pg_get_function_arguments(p.oid) as function_arguments,
       t.typname as return_type
from pg_proc p
left join pg_namespace n on p.pronamespace = n.oid
left join pg_language l on p.prolang = l.oid
left join pg_type t on t.oid = p.prorettype 
where n.nspname not in ('pg_catalog', 'information_schema')
)
    select *
    from tbl
    where definition ilike '%word or text you want to search%'
    order by function_schema,
             function_name;