Reading from blocking fifo pipe in shell script Post: 302116761

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LEARN ABOUT BSD

pipe

PIPE(2) 							System Calls Manual							   PIPE(2)

NAME

       pipe - create an interprocess communication channel

SYNOPSIS

       pipe(fildes)
       int fildes[2];

DESCRIPTION

       The pipe system call creates an I/O mechanism called a pipe.  The file descriptors returned can be used in read and write operations.  When
       the pipe is written using the descriptor fildes[1] up to 4096 bytes of data are buffered before the writing process is suspended.   A  read
       using the descriptor fildes[0] will pick up the data.

       It  is  assumed	that after the pipe has been set up, two (or more) cooperating processes (created by subsequent fork calls) will pass data
       through the pipe with read and write calls.

       The shell has a syntax to set up a linear array of processes connected by pipes.

       Read calls on an empty pipe (no buffered data) with only one end (all write file descriptors closed) returns an end-of-file.

       Pipes are really a special case of the socketpair(2) call and, in fact, are implemented as such in the system.

       A signal is generated if a write on a pipe with only one end is attempted.

RETURN VALUE

       The function value zero is returned if the pipe was created; -1 if an error occurred.

ERRORS

       The pipe call will fail if:

       [EMFILE]       Too many descriptors are active.

       [ENFILE]       The system file table is full.

       [EFAULT]       The fildes buffer is in an invalid area of the process's address space.

SEE ALSO

       sh(1), read(2), write(2), fork(2), socketpair(2)

BUGS

       Should more than 4096 bytes be necessary in any pipe among a loop of processes, deadlock will occur.

4th Berkeley Distribution					  August 26, 1985							   PIPE(2)

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