getExePath.hs

module Main where

import Foreign.C
import Foreign.Marshal.Alloc
import Foreign.Ptr
import Foreign.Storable
import System.Posix.Internals

-- import System.Environment (getExecutablePath)

main :: IO ()
main = print =<< getExecutablePath

foreign import ccall unsafe "getFullProgArgv"
    c_getFullProgArgv :: Ptr CInt -> Ptr (Ptr CString) -> IO ()

getExecutablePath :: IO FilePath
getExecutablePath =
    alloca $ \ p_argc ->
    alloca $ \ p_argv -> do
        c_getFullProgArgv p_argc p_argv
        argc <- peek p_argc
        if argc > 0
            -- If argc > 0 then argv[0] is guaranteed by the standard
            -- to be a pointer to a null-terminated string.
            then peek p_argv >>= peek >>= peekFilePath
            else errorWithoutStackTrace $ "getExecutablePath: " ++ msg
  where msg = "no OS specific implementation and program name couldn't be " ++
              "found in argv"