[Haskell-cafe] Re: dangling symbolic links

[Nicolas Frisby]

Ah the magic of using a mailing list... I just realized that using
getDirectoryContents lists the entry.

Still, a "doesLinkExist" function might be nice...

On Wed, Aug 27, 2008 at 11:46 PM, Nicolas Frisby
<nicolas.frisby at gmail.com> wrote:
> I think I've exhausted my options without catching exceptions.
>
> If I have an invalid symbolic link, how can I identify that it exists?
>
> (Sorry about the line wrap.)
>
> tmp$ ls -l            # no tricks up my sleeve, empty directory
> tmp$ touch foo
> tmp$ ln -s foo bar
> tmp$ ls -l
> total 8
> lrwxr-xr-x   1 nfrisby  nfrisby  3 Aug 27 23:29 bar -> foo
> -rw-r--r--   1 nfrisby  nfrisby  0 Aug 27 23:29 foo
> tmp$ ghc -e 'System.Directory.doesFileExist "bar"'
> True
> tmp$ rm foo
> tmp$ ls -l
> total 8
> lrwxr-xr-x   1 nfrisby  nfrisby  3 Aug 27 23:29 bar -> foo
> tmp$ ghc -e 'System.Directory.doesFileExist "bar"'      # it follows
> the broken link
> False
> tmp$ ghc -e 'System.Posix.Files.fileExist "bar"'            # the
> POSIX API also follows
> False
> tmp$ ghc -e 'System.Posix.Files.isSymbolicLink `fmap`
> System.Posix.Files.getFileStatus "bar"'  # so does this one POSIX API
> also follows
> *** Exception: bar: getFileStatus: does not exist (No such file or directory)
> tmp$ ghc -e 'System.Posix.Files.isSymbolicLink `fmap`
> System.Posix.Files.getSymbolicLinkStatus "bar"'   # the most
> successful so far
> True
> tmp$ rm bar  # but it isn't an existence check...
> tmp$ ls -l
> tmp$ ghc -e 'System.Posix.Files.isSymbolicLink `fmap`
> System.Posix.Files.getSymbolicLinkStatus "bar"'
> *** Exception: bar: getSymbolicLinkStatus: does not exist (No such
> file or directory)
>
> Is there a way to check for the existence of a symbolic link without
> testing if getSymbolicLinkStatus raises an exception?
>
> This is with Darwin Kernel Version 8.11.1, GHC 6.8.2,
> directory-1.0.0.0, and unix-2.3.0.0.
>
> Thanks.
>