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shapr/Env.hs

Created September 7, 2019 20:54
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lookup environment variables, some of which do not exist. Handle whether exists or not.
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Env.hs
module Main where
-- using http://hackage.haskell.org/package/base-4.12.0.0/docs/System-Environment.html#v:lookupEnv
import System.Environment
main :: IO ()
main = do
shell <- lookupEnv "SHELL" -- System.Environment.lookupEnv take a String
doesnotexist <- lookupEnv "DOESNOTEXIST"
print (checkEnvVars shell)
print (checkEnvVars doesnotexist)
checkEnvVars :: Maybe String -> String
checkEnvVars Nothing = "This value does not exist"
checkEnvVars (Just v) = "The enviroment has this, value is " <> v
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