Using local variable in psql cli or declare and append in procedure (Postgresql) [duplicate] - sql

Question

Here's what I would like to do:
\set values foo,bar,baz
DO $$
DECLARE
value TEXT;
values TEXT[] := string_to_array(:'values', ',');
BEGIN
FOREACH value IN ARRAY values LOOP
raise notice 'v: %', value;
END LOOP;
END $$ LANGUAGE plpgsql;
Which results in the following error:
ERROR: syntax error at or near ":"
SELECT string_to_array(:'values', ',') INTO values...
^
Here's the solution I have currently, but it feels hacky:
\set values foo,bar,baz
PREPARE get_values AS SELECT string_to_array(:'values', ',');
DO $$
DECLARE
value TEXT;
values TEXT[];
BEGIN
EXECUTE 'EXECUTE get_values' INTO values;
FOREACH value IN ARRAY values LOOP
raise notice 'v: %', value;
END LOOP;
END $$ LANGUAGE plpgsql;

Answer 1

Answer
DO expects a string literal with plpgsql code. Symbols are not substituted inside strings in psql.
You could concatenate the whole string into a psql variable and then execute it.
How to concatenate psql variables?
Pretty multi-line format is not possible, because (per documentation):
But in any case, the arguments of a meta-command cannot continue
beyond the end of the line.
Simple example:
test=# \set value foo
test=# \set do 'BEGIN\n RAISE NOTICE ''v: %'', ' :'value' ';\nEND'
test=# DO :'do';
NOTICE: v: foo
Replace line breaks with \n (or remove them if you don't care for pretty format). Based on this adapted code:
DO
'
DECLARE
_val text;
_vals text[] := string_to_array(>>values<<, '','');
BEGIN
FOREACH _val IN ARRAY _vals
LOOP
RAISE NOTICE ''v: %'', _val;
END LOOP;
END
'
It looks like this:
test=# \set do 'DECLARE\n _val text;\n _vals text[] := string_to_array(' :'values' ', '','');\nBEGIN\n FOREACH _val IN ARRAY _vals\n LOOP\n RAISE NOTICE ''v: %'', _val;\n END LOOP;\nEND'
test=# DO :'do';
NOTICE: v: foo
NOTICE: v: bar
NOTICE: v: baz
DO
I added bold emphasis to the variable to make it easier to spot.
Related answer by #Pavel (ab)using a server session variable:
Referring to session variables (\set var='value') from PL/PGSQL
Alternative solutions
Prepared statement
Your current solution doesn't look that bad. I would simplify:
PREPARE get_values AS SELECT * FROM regexp_split_to_table(:'values', ',');
DO
$do$
DECLARE
_val text;
BEGIN
FOR _val IN EXECUTE
'EXECUTE get_values'
LOOP
RAISE NOTICE 'v: %', _val;
END LOOP;
END
$do$;
Temporary table
Similar solution with a temporary table:
CREATE TEMP TABLE tmp AS SELECT * FROM regexp_split_to_table(:'values', ',') v;
DO
$do$
DECLARE
_val text;
BEGIN
FOR _val IN
TABLE tmp
LOOP
RAISE NOTICE 'v: %', _val;
END LOOP;
END
$do$;

Answer 2

Was able to take advantage of this solution:
Passing argument to a psql procedural script
Where I set the variable as such and retrieve it with current_setting()
\set values foo,bar,baz
SET vars.values TO :'values';
DO $$
DECLARE
value TEXT;
values TEXT[] := string_to_array(current_setting('vars.values'), ',');
BEGIN
FOREACH value IN ARRAY values LOOP
RAISE NOTICE 'v: %', value;
END LOOP;
END $$ LANGUAGE plpgsql