filelib:is_* is missing something necessary.

Michael Richter ttmrichter@REDACTED
Sat Nov 28 15:09:36 CET 2009

I found out that the file type predicates in *filelib* (*is_file/1*, *
is_dir/1*, *is_regular/1*) have a little quirk that makes them not that
useful for my purposes.  Specifically they treat symbolic links to files as
files and symbolic links to directories as directories instead of flagging
each respectively as symlinks.

It seems to me that they're implemented in terms of
*read_file_info/1*instead of
*read_link_info/1* and I was wondering if it might not be possible to make
one of the following changes, depending on what people in the community
found most useful (I'm easy either way, personally):

   1. Change the return values such that, say, *is_file/1* returns *true* if
   the named file is a straight file, but returns *symlink* if it is a
   symbolic link *to a file*.  (In any other situation -- directory, symlink
   to directory, special file, etc. -- it would still return *false*.)
   2. Add a predicate *is_symlink/1* so that I can first check if
   something's a directory and then follow through with a check if it's a
   symbolic link to one.

Currently I've just rewritten the predicates for my code, but in general I
prefer to use system libraries wherever possible so I'd really like to see
one of the two above approaches (or perhaps a third, superior one) written
in.  My predicate for *is_symlink/1* looks like this:

is_symlink(Name) ->
    case file:read_link_info(Name) of
        {ok, FileInfo} -> FileInfo#file_info.type =:= symlink

It's not a particularly Earth-shattering change for option 2.  Option 1
could look something like this only without the fugliness of my quick hack.:

is_regular(Name) ->
    case file:read_file_info(Name) of
        {ok, #file_info{type = regular}} ->
            case file:read_link_info(Name) of
                {ok, #file_info{type = symlink}} -> symlink;
                _                                -> true
        _                                -> false

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