marc@athena.mit.edu (Marc Horowitz) (02/24/91)
I know this has been mentioned here before, but I don't remember what the reasons were. Why is open(FOO,"|cat|") (a pipe to a program which I can read from and write to) not supported? If a patch were to land in your mailbox, Larry, would you consider taking it? If so, I might consider writing it. The reason I want this is because I have a remote database server, and a client which accepts "operation arg1 arg2 ..." as input, and gives whitespace separated fields as a response. I'd like to open a pipe to this process so I can write queries and read back responses. For now, I can use pipe, fork, and exec, but having this functionality in open is a lot more elegant, even if it isn't necessarily portable (like to MS-DOS). Marc
tchrist@convex.COM (Tom Christiansen) (02/25/91)
I think that making "|foo|" be a two-way pipe would be giving the novice enough rope to hang himself. He would not understand why his programs didn't work. By the time he understands files enough to know why this simplistic approach is so perilous, if he still wants one, he can either cobble together his own version or pull out &open2() from the FAQ. --tom -- "UNIX was not designed to stop you from doing stupid things, because that would also stop you from doing clever things." -- Doug Gwyn Tom Christiansen tchrist@convex.com convex!tchrist
ea08+@andrew.cmu.edu (Eric A. Anderson) (02/28/91)
marc@athena.mit.edu (Marc Horowitz) writes: > |> From the keyboard of marc@mit.edu: > |> :I know this has been mentioned here before, but I don't remember what > |> :the reasons were. Why is open(FOO,"|cat|") (a pipe to a program which > |> :I can read from and write to) not supported? > |> > |> From the FAQ: > |> > |> 20) How do I open a pipe both to and from a command? > |> > |> In general, this is a dangerous move because you can find yourself in > |> deadlock situation. It's better to put one end of the pipe to a file. For whatever reason, I found that open(FOO,'ftp |'); allowed me to do both writes and reads from FOO. Is this a mis-feature or something? Because I find this fundamentaly useful, I want a program which can do things with ftp sessions. (Primarily, get all files under some directory subject to certain constraints.) The only other way to do this would be to write a C program containing all of ftp which seems like overkill. Am I in risk of a deadlock or something? -Eric ********************************************************* "My life is full of additional complications spinning around until it makes my head snap off." -Unc. Known. "You are very smart, shut up." -In "The Princess Bride" *********************************************************
lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall) (03/02/91)
In article <Mbn9n5G00VQoA9qdhX@andrew.cmu.edu> ea08+@andrew.cmu.edu (Eric A. Anderson) writes:
: For whatever reason, I found that open(FOO,'ftp |'); allowed me to do
: both writes and reads from FOO. Is this a mis-feature or something?
Uh, you might well be able to write to the input pipe if it's implemented
as a socket or stream, but the real question is why ftp would be reading
its stdout. Are you actually able to interact with ftp this way? Weird.
ftp's stdin should be hooked up to whatever stdin your perl script is using.
: Because I find this fundamentaly useful, I want a program which can do
: things with ftp sessions. (Primarily, get all files under some
: directory subject to certain constraints.) The only other way to do
: this would be to write a C program containing all of ftp which seems
: like overkill. Am I in risk of a deadlock or something?
Not likely with ftp, as long as you stay in sync and read everything there
is to read before going on to the next command.
Larryallbery@NCoast.ORG (Brandon S. Allbery KB8JRR) (03/02/91)
As quoted from <1991Feb23.205035.21729@convex.com> by tchrist@convex.COM (Tom Christiansen): +--------------- | From the keyboard of marc@mit.edu: | :I know this has been mentioned here before, but I don't remember what | :the reasons were. Why is open(FOO,"|cat|") (a pipe to a program which | :I can read from and write to) not supported? | | From the FAQ: | | 20) How do I open a pipe both to and from a command? | | In general, this is a dangerous move because you can find yourself in | deadlock situation. It's better to put one end of the pipe to a file. +--------------- True, but there is a class of programs designed to work this way (like some database servers, as marc@mit mentioned). ++Brandon -- Me: Brandon S. Allbery VHF/UHF: KB8JRR on 220, 2m, 440 Internet: allbery@NCoast.ORG Packet: KB8JRR @ WA8BXN America OnLine: KB8JRR AMPR: KB8JRR.AmPR.ORG [44.70.4.88] uunet!usenet.ins.cwru.edu!ncoast!allbery Delphi: ALLBERY