Reference psql parameter inside PL/pgSQL anonymous block - postgresql

Question

I'd like to pass a parameter to an anonymous PL/pgSQL block via psql command line, then check that parameter in a conditional.
The relevant part of the SQL is here:
do $$
begin
if (':para' = 1) then
-- statements;
end if;
end $$
;
I call this script as such:
psql -d dbname -v para=1 < script.sql
I receive the error:
ERROR: invalid input syntax for integer: ":para"
LINE 1: SELECT (':para' = 1)
^
QUERY: SELECT (':para' = 1)
CONTEXT: PL/pgSQL function inline_code_block line 3 at IF
I tried using the case/when paradigm, which did not work either.
I am guessing that a psql parameter is not compatible with PL/pgSQL? Ultimately, my goal is to run a single delete statement if I pass 1 as a psql parameter, and not run it if I pass 0.

Answer 1

The psql parser can't see what is inside strings. This might be what you want:
delete from t
where :para = 1
Do it outside of an anonymous block. If you really need PL/pgSQL use a parameterized function:
create or replace function f(_para integer)
returns void as $$
begin
if _para = 1 then
--statements
end if;
end; $$ language plpgsql;
And your script file will have:
select f(:para);
If you do not want to permanently add a function to the db do it all inside the script:
drop function if exists f_iu7YttW(integer);
create or replace function f_iu7YttW(_para integer)
returns void as $$
begin
if _para = 1 then
--statements
end if;
end; $$ language plpgsql;
select f_iu7YttW(:para);
drop function f_iu7YttW(integer);
Give the function an unique name so you do not run the risk of dropping something else.