Haskell: hSetFileSize: Truncate the file

hSetFileSize  takes a handle and an integer n as arguments and truncates the physical file with handle hdl to n bytes.

Prelude System.IO> :t hSetFileSize

hSetFileSize :: Handle -> Integer -> IO ()

Suppose today.txt contains following data.

$ cat today.txt
If you love a flower, don’t pick it up.
Because if you pick it up it dies and it ceases to be what you love.
So if you love a flower, let it be.
Love is not about possession.
Love is about appreciation.

Following program truncate the file to half of the size.

FileUtil.hs

import System.IO

main = 
    do
     putStrLn "Enter file name (Including full path) to read"
     fileName <- getLine

     handle <- openFile fileName ReadWriteMode   

     size <- hFileSize handle
     contents <- hGetContents handle

     putStrLn $ "Size is " ++ show size
     putStrLn $ "Content is : " ++ contents

     hClose handle

     handle1 <- openFile fileName ReadWriteMode
     hSetFileSize handle1 (size `div` 2)

     size1 <- hFileSize handle1
     contents1 <- hGetContents handle1

     putStrLn $ "Size is " ++ show size1
     putStrLn $ "Content is : " ++ contents1

     hClose handle1

$ ghc FileUtil.hs
[1 of 1] Compiling Main             ( FileUtil.hs, FileUtil.o )
Linking FileUtil ...
$
$ 
$ ./FileUtil
Enter file name (Including full path) to read
today.txt
Size is 206
Content is : If you love a flower, don’t pick it up.
Because if you pick it up it dies and it ceases to be what you love.
So if you love a flower, let it be.
Love is not about possession.
Love is about appreciation.


Size is 103
Content is : If you love a flower, don’t pick it up.
Because if you pick it up it dies and it ceases to be what yo
$ 
$ cat today.txt
If you love a flower, don’t pick it up.
Because if you pick it up it dies and it ceases to be what yo

Previous                                                 Next                                                 Home