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Top Forums Shell Programming and Scripting Reading from blocking fifo pipe in shell script Post 302116663 by victorin on Monday 7th of May 2007 12:40:40 PM
Old 05-07-2007
Reading from blocking fifo pipe in shell script

Hi!!

I have a problem reading from a fifo pipe in shell script.

The idea is simple, I have a C program with two pipe files:
  • An input pipe I use to send commands in shell script to the C program (echo "command" > input.pipe)
  • An output pipe that I read the result of the command also in shell script (cat output.pipe)

The problem is in the cat output.pipe
After output the data the cat process remains blocked (like a "tail -f") waiting for data.

It's possible to avoid this state?? (It's possible the cat terminates when the pipe not contains more data? Something like non-blocking read)

Thank you very much
 

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io_pipe(3)						     Library Functions Manual							io_pipe(3)

NAME
io_pipe - create a Unix pipe SYNTAX
#include <io.h> int io_pipe(int64 pfd[2]); DESCRIPTION
io_pipe creates a new UNIX ``pipe.'' The pipe can receive data and provide data; any bytes written to the pipe can then be read from the pipe in the same order. A pipe is typically stored in an 8192-byte memory buffer; the exact number depends on the UNIX kernel. Bytes are written to the end of the buffer and read from the beginning of the buffer. Once a byte has been read, it is eliminated from the buffer, making space for another byte to be written; readers cannot ``rewind'' a pipe to read old data. Once 8192 bytes have been written to the buffer, the pipe will not be ready for further writing until some of the bytes have been read. Once all the bytes written have been read, the pipe will not be ready for further reading until more bytes are written. io_pipe sets d[0] to the number of a new descriptor reading from the pipe, and sets d[1] to the number of a new descriptor writing to the pipe. It then returns 1 to indicate success. If something goes wrong, io_pipe returns 0, setting errno to indicate the error; in this case it frees any memory that it allocated for the new pipe, and it leaves d alone. SEE ALSO
io_readfile(3), io_createfile(3), io_socketpair(3) io_pipe(3)
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