Retaining data in a named pipe after an incomplete read access

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Prerequisites:



$ mkfifo pipe1


If several lines are put into pipe1



$ (echo line 1; echo line 2) > pipe1


all the lines can be read in another terminal by



$ cat pipe1
line 1
line 2


So far all right.



But



if instead of the latter cat several partial reads are executed



$ head -n 1 pipe1; head -n 1 pipe1
line 1


then only the first line of the data piped into pipe1 is returned (by the first head -n 1); the rest of the data seems to get lost, the second read access is hanging hence waiting for (new) data available in pipe1.



How



to set up a named pipe and pipe contents to it in such a way that several consecutive partial reads are possible?



In other words, how to get this:



$ head -n 1 pipe1; head -n 1 pipe1
line 1
line 2



io-redirection fifo




share|improve this question





















  • IIRC, but I may be wrong here, you can't close the pipe - this will flush the data. But head closes it. So you'll need a custom version of head that doesn't close it. Not very elegant. What are you trying to achieve with this? It sounds like an XY-Problem.
    – dirkt
    Jul 20 at 13:11











  • @dirk1 In the end I want to have a persistent FIFO queue: write arbitrary times to a file, read arbitrary times from the same file, data that is read disappears from the queue. Named pipes seemed to me like a solution for that. But as pointed out in the question, it does not work like expected by me.
    – Min-Soo Pipefeet
    Jul 20 at 13:18










  • Pipes won't work for this. See e.g. here for alternatives.
    – dirkt
    Jul 20 at 14:29
















up vote
1
down vote

favorite












Prerequisites:



$ mkfifo pipe1


If several lines are put into pipe1



$ (echo line 1; echo line 2) > pipe1


all the lines can be read in another terminal by



$ cat pipe1
line 1
line 2


So far all right.



But



if instead of the latter cat several partial reads are executed



$ head -n 1 pipe1; head -n 1 pipe1
line 1


then only the first line of the data piped into pipe1 is returned (by the first head -n 1); the rest of the data seems to get lost, the second read access is hanging hence waiting for (new) data available in pipe1.



How



to set up a named pipe and pipe contents to it in such a way that several consecutive partial reads are possible?



In other words, how to get this:



$ head -n 1 pipe1; head -n 1 pipe1
line 1
line 2



io-redirection fifo




share|improve this question





















  • IIRC, but I may be wrong here, you can't close the pipe - this will flush the data. But head closes it. So you'll need a custom version of head that doesn't close it. Not very elegant. What are you trying to achieve with this? It sounds like an XY-Problem.
    – dirkt
    Jul 20 at 13:11











  • @dirk1 In the end I want to have a persistent FIFO queue: write arbitrary times to a file, read arbitrary times from the same file, data that is read disappears from the queue. Named pipes seemed to me like a solution for that. But as pointed out in the question, it does not work like expected by me.
    – Min-Soo Pipefeet
    Jul 20 at 13:18










  • Pipes won't work for this. See e.g. here for alternatives.
    – dirkt
    Jul 20 at 14:29












up vote
1
down vote

favorite









up vote
1
down vote

favorite











Prerequisites:



$ mkfifo pipe1


If several lines are put into pipe1



$ (echo line 1; echo line 2) > pipe1


all the lines can be read in another terminal by



$ cat pipe1
line 1
line 2


So far all right.



But



if instead of the latter cat several partial reads are executed



$ head -n 1 pipe1; head -n 1 pipe1
line 1


then only the first line of the data piped into pipe1 is returned (by the first head -n 1); the rest of the data seems to get lost, the second read access is hanging hence waiting for (new) data available in pipe1.



How



to set up a named pipe and pipe contents to it in such a way that several consecutive partial reads are possible?



In other words, how to get this:



$ head -n 1 pipe1; head -n 1 pipe1
line 1
line 2



io-redirection fifo




share|improve this question













Prerequisites:



$ mkfifo pipe1


If several lines are put into pipe1



$ (echo line 1; echo line 2) > pipe1


all the lines can be read in another terminal by



$ cat pipe1
line 1
line 2


So far all right.



But



if instead of the latter cat several partial reads are executed



$ head -n 1 pipe1; head -n 1 pipe1
line 1


then only the first line of the data piped into pipe1 is returned (by the first head -n 1); the rest of the data seems to get lost, the second read access is hanging hence waiting for (new) data available in pipe1.



How



to set up a named pipe and pipe contents to it in such a way that several consecutive partial reads are possible?



In other words, how to get this:



$ head -n 1 pipe1; head -n 1 pipe1
line 1
line 2




io-redirection fifo





share|improve this question












share|improve this question




share|improve this question








edited Jul 20 at 13:11
























asked Jul 20 at 13:07









Min-Soo Pipefeet

1064




1064











  • IIRC, but I may be wrong here, you can't close the pipe - this will flush the data. But head closes it. So you'll need a custom version of head that doesn't close it. Not very elegant. What are you trying to achieve with this? It sounds like an XY-Problem.
    – dirkt
    Jul 20 at 13:11











  • @dirk1 In the end I want to have a persistent FIFO queue: write arbitrary times to a file, read arbitrary times from the same file, data that is read disappears from the queue. Named pipes seemed to me like a solution for that. But as pointed out in the question, it does not work like expected by me.
    – Min-Soo Pipefeet
    Jul 20 at 13:18










  • Pipes won't work for this. See e.g. here for alternatives.
    – dirkt
    Jul 20 at 14:29
















  • IIRC, but I may be wrong here, you can't close the pipe - this will flush the data. But head closes it. So you'll need a custom version of head that doesn't close it. Not very elegant. What are you trying to achieve with this? It sounds like an XY-Problem.
    – dirkt
    Jul 20 at 13:11











  • @dirk1 In the end I want to have a persistent FIFO queue: write arbitrary times to a file, read arbitrary times from the same file, data that is read disappears from the queue. Named pipes seemed to me like a solution for that. But as pointed out in the question, it does not work like expected by me.
    – Min-Soo Pipefeet
    Jul 20 at 13:18










  • Pipes won't work for this. See e.g. here for alternatives.
    – dirkt
    Jul 20 at 14:29















IIRC, but I may be wrong here, you can't close the pipe - this will flush the data. But head closes it. So you'll need a custom version of head that doesn't close it. Not very elegant. What are you trying to achieve with this? It sounds like an XY-Problem.
– dirkt
Jul 20 at 13:11





IIRC, but I may be wrong here, you can't close the pipe - this will flush the data. But head closes it. So you'll need a custom version of head that doesn't close it. Not very elegant. What are you trying to achieve with this? It sounds like an XY-Problem.
– dirkt
Jul 20 at 13:11













@dirk1 In the end I want to have a persistent FIFO queue: write arbitrary times to a file, read arbitrary times from the same file, data that is read disappears from the queue. Named pipes seemed to me like a solution for that. But as pointed out in the question, it does not work like expected by me.
– Min-Soo Pipefeet
Jul 20 at 13:18




@dirk1 In the end I want to have a persistent FIFO queue: write arbitrary times to a file, read arbitrary times from the same file, data that is read disappears from the queue. Named pipes seemed to me like a solution for that. But as pointed out in the question, it does not work like expected by me.
– Min-Soo Pipefeet
Jul 20 at 13:18












Pipes won't work for this. See e.g. here for alternatives.
– dirkt
Jul 20 at 14:29




Pipes won't work for this. See e.g. here for alternatives.
– dirkt
Jul 20 at 14:29















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