System.ReadEnvVar

This Haskell module exports functions for safely reading environment variables.

Documentation

readEnvVar

Arguments

:: Read a

=> String

environment variable to lookup

-> IO (Maybe a)

Lookup a value from an environment variable and read it in with readMaybe.

>>> import System.Environment (setEnv)
>>> setEnv "TEST_ENV_VAR" "2000"
>>> readEnvVar "TEST_ENV_VAR" :: IO (Maybe Int)
Just 2000
>>> readEnvVar "THIS_ENV_VAR_WILL_NOT_EXIST" :: IO (Maybe Int)
Nothing

readEnvVarDef

Arguments

:: Read a

=> String

environment variable to lookup

-> a

default value to use if the environment variable either does not exist, or cannot be read

-> IO a

Lookup a value from an environment variable and read it in with readMaybe. If the environment variable doesn't exist, or it can't be read, use the default value.

>>> import System.Environment (setEnv)
>>> setEnv "TEST_ENV_VAR" "1000"
>>> readEnvVarDef "TEST_ENV_VAR" 5 :: IO Int
1000
>>> readEnvVarDef "THIS_ENV_VAR_WILL_NOT_EXIST" 5 :: IO Int
5