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Date: Tue, 21 Jan 2003 14:42:08 -0800
From: Issac Trotts <ijtrotts@ucdavis.edu>
To: OCaml Mailing List <caml-list@inria.fr>
Subject: Re: [Caml-list] uname for Ocaml
Message-ID: <20030121224208.GA8872@beech>
References: <15917.26071.995917.528195@hector.lesours> <20030121202955.GA5938@beech> <15917.45880.856573.222243@hector.lesours>
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On Tue, Jan 21, 2003 at 09:53:12PM +0100, Basile STARYNKEVITCH wrote:
> 
> Issac cited me after his reply - I put it in the right order.
> 
> >>>>> "Issac" == Issac Trotts <ijtrotts@ucdavis.edu> writes:
> 
> 
> 
>     Issac> On Tue, Jan 21, 2003 at 04:23:03PM +0100, Basile
>     Issac> STARYNKEVITCH wrote:
>     >> Dear All,
>     >> 
>     >> If you need to call uname(2) from some Ocaml program you can
>     >> steal my tiny code in util.ml util.mli util_ml.c on
>     >> 
>     >> http://www2.poesia-filter.org:8000/cgi-bin/cvsweb.cgi/PoesiaSoft/PoesiaMonIcap/
>     >> 
>     >> I actually wish that uname(2) will be incorporated in the Unix
>     >> module.
>     >> 
> 
> 
>     Issac> An alternative would be to use #load "unix.cma"
> 
> I agree with Issac, but I still wish that most (or perhaps all) of the
> standard Posix system calls should be callable from Unix module!
> 
>     Issac>   let uname() = let (inc, outc) = Unix.open_process "uname"
>     Issac> in let name = input_line inc in close_in inc; close_out
>     Issac> outc; name;;
> 
> Won't work if the (malicious) user have an unrelated uname in his
> path. I suggest at least using the "/bin/uname" which should be a
> POSIX standard IIRC. Also, forking a shell process for each system
> call might be not optimal (and not robust).
> 
> Also, my code return the equivalent of /bin/uname -a
> 
>     Issac> Here's a more general way to capture the stdout of a Unix
>     Issac> call:
> 
>     Issac>   let syscall cmd = let (inc, outc) = Unix.open_process cmd
>     Issac> in let buf = Buffer.create 16 in (try while true do
>     Issac> Buffer.add_channel buf inc 1 done with _ -> ()); close_in
>     Issac> inc; close_out outc; Buffer.contents buf;;
> 
> Thanks for this suggestion, but why not use Unix.open_process_in in
> this and similar cases?

You're right: it's shorter to say

  let sys_call cmd =                                                     
    let inc = Unix.open_process_in cmd in
    let buf = Buffer.create 16 in
    (try while true do Buffer.add_channel buf inc 1 done with _ -> ());
    close_in inc;
    Buffer.contents buf;;

Or we can break the call results into lines:

  let rec input_lines file =                                                  
    try  
      let ln = input_line file in
      ln :: input_lines file
    with
      End_of_file -> [];;
  
  let sys_lines cmd =
    let pipe = Unix.open_process_in cmd in
    let lines = input_lines pipe in
    close_in f;
    lines;;

Sometimes it would be better to iterate a function over the lines:

  let sys_iter f cmd =
    let pipe = Unix.open_process_in cmd in
    (try while true do f (input_line pipe) done with _ -> ());
    close_in pipe;;
    
This can be used for things like
  
  sys_iter print_endline "ls";;

Issac

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