Using exec 3> to keep a named pipe open
The process reading from a named pipe will normally terminate when the process writing to the pipe finishes writing (sends an EOF). In certain situations you may have different processes writing intermittently to the pipe, and want a single process to continuously read from the pipe. To do this you can set up a 'dummy' writer that opens the pipe but doesn't write to it:
$ mkfifo myPipe
$ cat > myPipe &
The dummy writer keeps the named pipe open — without feeding data into it or ever closing. The reader process is thus able to receive input from all of the (other) legitimate writers without terminating and having to be respawned.
I have seen some folks use exec 3> instead of cat as a way to keep the named pipe open.
$ mkfifo myPipe
$ cat < myPipe &
[1] 10796
$ exec 3> myPipe
$ echo "blah" > myPipe
blah
This approach seems to work, and you don't have a dummy writer in the background to worry about (or clean up), so I like it. The problem is that I don't really understand it.
Can anyone help me understand exactly how exec 3> is accomplishing the task of keeping the named pipe open without an actual file to be executed, or a visible (background) process, and are there any downsides to this approach?
(I know that it must ultimately be opening the named pipe's input file descriptor for writing, so I'm specifically interested in what the exec 3 part of exec 3> is doing.)
exec fifo
asked 2 mins ago
TimTim
28128
add a comment |
The process reading from a named pipe will normally terminate when the process writing to the pipe finishes writing (sends an EOF). In certain situations you may have different processes writing intermittently to the pipe, and want a single process to continuously read from the pipe. To do this you can set up a 'dummy' writer that opens the pipe but doesn't write to it:
$ mkfifo myPipe
$ cat > myPipe &
The dummy writer keeps the named pipe open — without feeding data into it or ever closing. The reader process is thus able to receive input from all of the (other) legitimate writers without terminating and having to be respawned.
I have seen some folks use exec 3> instead of cat as a way to keep the named pipe open.
$ mkfifo myPipe
$ cat < myPipe &
[1] 10796
$ exec 3> myPipe
$ echo "blah" > myPipe
blah
This approach seems to work, and you don't have a dummy writer in the background to worry about (or clean up), so I like it. The problem is that I don't really understand it.
Can anyone help me understand exactly how exec 3> is accomplishing the task of keeping the named pipe open without an actual file to be executed, or a visible (background) process, and are there any downsides to this approach?
(I know that it must ultimately be opening the named pipe's input file descriptor for writing, so I'm specifically interested in what the exec 3 part of exec 3> is doing.)
exec fifo
asked 2 mins ago
TimTim
28128
add a comment |
The process reading from a named pipe will normally terminate when the process writing to the pipe finishes writing (sends an EOF). In certain situations you may have different processes writing intermittently to the pipe, and want a single process to continuously read from the pipe. To do this you can set up a 'dummy' writer that opens the pipe but doesn't write to it:
$ mkfifo myPipe
$ cat > myPipe &
The dummy writer keeps the named pipe open — without feeding data into it or ever closing. The reader process is thus able to receive input from all of the (other) legitimate writers without terminating and having to be respawned.
I have seen some folks use exec 3> instead of cat as a way to keep the named pipe open.
$ mkfifo myPipe
$ cat < myPipe &
[1] 10796
$ exec 3> myPipe
$ echo "blah" > myPipe
blah
This approach seems to work, and you don't have a dummy writer in the background to worry about (or clean up), so I like it. The problem is that I don't really understand it.
Can anyone help me understand exactly how exec 3> is accomplishing the task of keeping the named pipe open without an actual file to be executed, or a visible (background) process, and are there any downsides to this approach?
(I know that it must ultimately be opening the named pipe's input file descriptor for writing, so I'm specifically interested in what the exec 3 part of exec 3> is doing.)
exec fifo
asked 2 mins ago
TimTim
28128
The process reading from a named pipe will normally terminate when the process writing to the pipe finishes writing (sends an EOF). In certain situations you may have different processes writing intermittently to the pipe, and want a single process to continuously read from the pipe. To do this you can set up a 'dummy' writer that opens the pipe but doesn't write to it:
$ mkfifo myPipe
$ cat > myPipe &
The dummy writer keeps the named pipe open — without feeding data into it or ever closing. The reader process is thus able to receive input from all of the (other) legitimate writers without terminating and having to be respawned.
I have seen some folks use exec 3> instead of cat as a way to keep the named pipe open.
$ mkfifo myPipe
$ cat < myPipe &
[1] 10796
$ exec 3> myPipe
$ echo "blah" > myPipe
blah
This approach seems to work, and you don't have a dummy writer in the background to worry about (or clean up), so I like it. The problem is that I don't really understand it.
Can anyone help me understand exactly how exec 3> is accomplishing the task of keeping the named pipe open without an actual file to be executed, or a visible (background) process, and are there any downsides to this approach?
(I know that it must ultimately be opening the named pipe's input file descriptor for writing, so I'm specifically interested in what the exec 3 part of exec 3> is doing.)
exec fifo
exec fifo
asked 2 mins ago
TimTim
28128
asked 2 mins ago
TimTim
28128
asked 2 mins ago
TimTim
28128
asked 2 mins ago
TimTim
28128
asked 2 mins ago
TimTim
28128
28128
add a comment |
add a comment |
0
active
oldest
votes
Your Answer
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "106"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f496810%2fusing-exec-3-to-keep-a-named-pipe-open%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
0
active
oldest
votes
0
active
oldest
votes
active
oldest
votes
active
oldest
votes
Thanks for contributing an answer to Unix & Linux Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f496810%2fusing-exec-3-to-keep-a-named-pipe-open%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
