Use `\gset` in psql to store the result of a query in a local variable - like dezso already advised. Shorter yet, `\gset` can replace the semicolon (`;`) as query terminator:

    test=# SELECT count(*) AS list FROM department.master_data \gset

Then, to get a single-quoted string (with any contained single quotes safely escaped automatically)  refer to the psql variable with this syntax variant: **`:'list'`**. Note the enclosing **`''`** *after* the colon!

    test=# COMMENT ON TABLE department.master_data IS :'list';

Read about [SQL interpolation in the manual][1].

Related:

- https://dba.stackexchange.com/questions/139681/create-sequence-using-expressions-with-psql-variables-for-parameters/139811#139811

  [1]: https://www.postgresql.org/docs/current/app-psql.html#APP-PSQL-INTERPOLATION