pipe(2)                                                                pipe(2)



NAME
     pipe - create an interprocess channel

C SYNOPSIS
     #include <unistd.h>

     int pipe(int fildes[2]);

DESCRIPTION
     pipe creates an I/O mechanism called a pipe and returns two file
     descriptors, fildes[0] and fildes[1].  IRIX has two distinct versions of
     pipe: the SVR4 version and the SVR3.2 version.  The SVR3.2 version is
     faster, and is generally preferred unless STREAMS semantics are required
     for a specific reason.

     The SVR4 version of pipe returns two STREAMS-based file descriptors which
     are both opened for reading and writing.  The ONDELAY and ONONBLOCK
     flags are cleared.  A read from fildes[0] accesses the data written to
     fildes[1] on a first-in-first-out (FIFO) basis and a read from fildes[1]
     accesses the data written to fildes[0] also on a FIFO basis.  The
     FDCLOEXEC flag will be clear on both file descriptors.

     The SVR3.2 version of pipe returns two non-STREAMS-based file
     descriptors.  Fildes[0] is opened for reading and fildes[1] is opened for
     writing.  Up to PIPEBUF (defined in limits.h) bytes of data are buffered
     by the pipe before the writing process is blocked and guaranteed to be
     written atomically.  The ONDELAY and ONONBLOCK flags are cleared.  A
     read only file descriptor fildes[0] accesses the data written to
     fildes[1] on a first-in-first-out (FIFO) basis.

     Upon successful completion pipe marks for update the statime, stctime,
     and stmtime fields of the pipe.

     To use the SVR4 version of pipe one must normally tune the system tunable
     variable svr3pipe to 0 (see systune(1M)).  Otherwise, the SVR3.2 version
     of pipe is used, with the exception of applications linked against
     libnsl.so (-lnsl), which normally get SVR4-style pipes by default.  This
     can be disabled by setting the environment variable LIBNSLUSESVR3PIPE
     to 1.  In this case such applications will get SVR3.2-styl pipe
     semantics.

     pipe fails if:

     EMFILE         The maximum number of file descriptors are currently open.

     ENFILE         A file table entry could not be allocated.

SEE ALSO
     sh(1), systune(1M), fcntl(2), getmsg(2), intro(3N), poll(2), putmsg(2),
     read(2), write(2), popen(3S), streamio(7)





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pipe(2)                                                                pipe(2)



DIAGNOSTICS
     Upon successful completion, a value of 0 is returned.  Otherwise, a value
     of -1 is returned and errno is set to indicate the error.

NOTES
     Since a SVR4 version of pipe is bi-directional, there are two separate
     flows of data.  Therefore, the size (stsize) returned by a call to
     fstat(2) with argument fildes[0] or fildes[1] is the number of bytes
     available for reading from fildes[0] or fildes[1] respectively.
     Previously, the size (stsize) returned by a call to fstat() with
     argument fildes[1] (the write-end) was the number of bytes available for
     reading from fildes[0] (the read-end).











































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