scroll-1.20250228.2: unix/Pager.hs

{-# LANGUAGE CPP #-}
module Pager where

import System.IO
import System.Posix.IO
import System.Posix.Terminal
import Control.Applicative
import Prelude

-- If stdin is not connected to a tty, we're being used as a pager with
-- output piped in. The content of stdin is sucked in and returned for
-- paging, and stdin is re-opened from the terminal device.
stdinPager :: IO (Maybe String)
stdinPager = go =<< queryTerminal stdInput
  where
	go True = return Nothing
	go False = do
		stdoutisterm <- queryTerminal stdOutput
		if stdoutisterm
			then do
				term <- getTerminalName stdOutput
				oldstdin <- dup stdInput
				closeFd stdInput
#if MIN_VERSION_unix(2,8,0)
				newstdin <- openFd term ReadOnly defaultFileFlags 
#else
				newstdin <- openFd term ReadOnly Nothing defaultFileFlags 
#endif
				_ <- dupTo newstdin stdInput
				Just <$> (hGetContents =<< fdToHandle oldstdin)
			else error "stdout is not a terminal"