Look up Postgres connection parameters from environment variables

Retrieves database connection parameters stored in any of the environment variables known by Postgres, using defaults from `...` for parameters not set in the environment. In a standard PEcAn installation only a few of these parameters will ever be set, but we check all of them anyway in case you need to do anything unusual.

get_postgres_envvars(...)

Arguments

...

defaults for parameters not found in the environment, in `name = value` form

Value

list of connection parameters suitable for passing on to `db.open`

Details

The list of environment variables we check is taken from the [Postgres 12 manual](https://postgresql.org/docs/12/libpq-envars.html), but it should apply to older Postgres versions as well. Note that this function only looks for environment variables that control connection parameters; it does not retrieve any of the variables related to per-session behavior (e.g. PGTZ, PGSYSCONFDIR).

Examples

 host <- Sys.getenv("PGHOST") # to restore environment after demo

 Sys.unsetenv("PGHOST")
 get_postgres_envvars()$host # NULL
#> NULL
 get_postgres_envvars(host = "default", port = 5432)$host # "default"
#> [1] "default"
 # defaults are ignored for a variable that exists
 Sys.setenv(PGHOST = "localhost")
 get_postgres_envvars()$host # "localhost"
#> [1] "localhost"
 get_postgres_envvars(host = "postgres")$host # still "localhost"
#> [1] "localhost"

 # To override a set variable, edit the returned list before using it
 con_parms <- get_postgres_envvars()
 con_parms$host # "localhost"
#> [1] "localhost"
 con_parms$host <- "postgres"
 # db.open(con_parms)

 Sys.setenv(PGHOST = host)