PIPE(2)                          System Calls                          PIPE(2)

NAME

       pipe - create descriptor pair for interprocess communication

SYNOPSIS

       #include <unistd.h>

       int pipe (int *fildes);

DESCRIPTION

       The pipe function creates a pipe, which is an object allowing unidirec‐
       tional data flow, and allocates a pair of file descriptors.  The  first
       descriptor  connects  to  the read end of the pipe, and the second con‐
       nects to the write end, so that data written to  fildes[1]  appears  on
       (i.e., can be read from) fildes[0].  This allows the output of one pro‐
       gram to be sent to another program: The source's standard output is set
       up  to  be  the write end of the pipe, and the sink's standard input is
       set up to be the read end of the pipe.  The pipe itself persists  until
       all its associated descriptors are closed.

       A  pipe  whose read or write end has been closed is considered widowed.
       Writing on such a pipe causes the writing process to receive a  SIGPIPE
       signal.   Widowing  a  pipe is the only way to deliver end-of-file to a
       reader: after the reader consumes any buffered data, reading a  widowed
       pipe returns a zero count (end of file).

LIMITS

       Up  to  4096  bytes  of data are buffered before the writing process is
       suspended.  Should more than 4096 bytes be necessary in any pipe  among
       a  loop  of  processes,  deadlock will occur.  This is not a limitation
       specific to GNO but to multiprogramming in general.

NOTES

       This man page refers to the Unix read(2) and write(2)  operations.   On
       the  IIgs,  the described behavior refer to any system calls doing I/O,
       including:
              GS/OS ReadGS and WriteGS
              TextTools calls
              C stdio I/O routines

RETURN VALUES

       On successful creation of the pipe,  zero  is  returned.  Otherwise,  a
       value  of -1 is returned and the variable errno set to indicate the er‐
       ror.

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)

HISTORY

       A pipe function call appeared in Version 6 AT&T UNIX.



GNO                             16 January 1997                        PIPE(2)