1PIPE(3P)                   POSIX Programmer's Manual                  PIPE(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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11

NAME

13       pipe — create an interprocess channel
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SYNOPSIS

16       #include <unistd.h>
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18       int pipe(int fildes[2]);
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DESCRIPTION

21       The pipe() function shall create a pipe and place two file descriptors,
22       one  each into the arguments fildes[0] and fildes[1], that refer to the
23       open file descriptions for the read and write ends of the  pipe.  Their
24       integer  values  shall  be  the two lowest available at the time of the
25       pipe() call. The O_NONBLOCK and FD_CLOEXEC flags shall be clear on both
26       file  descriptors.  (The fcntl() function can be used to set both these
27       flags.)
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29       Data can be written to the file descriptor fildes[1] and read from  the
30       file  descriptor  fildes[0].   A  read on the file descriptor fildes[0]
31       shall access data written to the file descriptor fildes[1] on a  first-
32       in-first-out  basis.  It  is unspecified whether fildes[0] is also open
33       for writing and whether fildes[1] is also open for reading.
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35       A process has the pipe open for reading (correspondingly writing) if it
36       has  a  file  descriptor  open  that  refers to the read end, fildes[0]
37       (write end, fildes[1]).
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39       The pipe's user ID shall be set to the effective user ID of the calling
40       process.
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42       The pipe's group ID shall be set to the effective group ID of the call‐
43       ing process.
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45       Upon successful completion, pipe() shall mark for update the last  data
46       access,  last data modification, and last file status change timestamps
47       of the pipe.
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RETURN VALUE

50       Upon successful completion, 0 shall be returned; otherwise, −1 shall be
51       returned and errno set to indicate the error.
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ERRORS

54       The pipe() function shall fail if:
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56       EMFILE All,  or  all  but one, of the file descriptors available to the
57              process are currently open.
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59       ENFILE The number of simultaneously open  files  in  the  system  would
60              exceed a system-imposed limit.
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62       The following sections are informative.
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EXAMPLES

65   Using a Pipe to Pass Data Between a Parent Process and a Child Process
66       The  following  example demonstrates the use of a pipe to transfer data
67       between a parent  process  and  a  child  process.  Error  handling  is
68       excluded, but otherwise this code demonstrates good practice when using
69       pipes: after the fork() the two processes close the unused ends of  the
70       pipe before they commence transferring data.
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72           #include <stdlib.h>
73           #include <unistd.h>
74           ...
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76           int fildes[2];
77           const int BSIZE = 100;
78           char buf[BSIZE];
79           ssize_t nbytes;
80           int status;
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82           status = pipe(fildes);
83           if (status == −1 ) {
84               /* an error occurred */
85               ...
86           }
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88           switch (fork()) {
89           case −1: /* Handle error */
90               break;
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92           case 0:  /* Child - reads from pipe */
93               close(fildes[1]);                       /* Write end is unused */
94               nbytes = read(fildes[0], buf, BSIZE);   /* Get data from pipe */
95               /* At this point, a further read would see end of file ... */
96               close(fildes[0]);                       /* Finished with pipe */
97               exit(EXIT_SUCCESS);
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99           default:  /* Parent - writes to pipe */
100               close(fildes[0]);                       /* Read end is unused */
101               write(fildes[1], "Hello world\n", 12);  /* Write data on pipe */
102               close(fildes[1]);                       /* Child will see EOF */
103               exit(EXIT_SUCCESS);
104           }
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APPLICATION USAGE

107       None.
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RATIONALE

110       The  wording  carefully  avoids  using the verb ``to open'' in order to
111       avoid any implication of use of open(); see also write().
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FUTURE DIRECTIONS

114       None.
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SEE ALSO

117       fcntl(), read(), write()
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119       The Base Definitions volume of POSIX.1‐2008, <fcntl.h>, <unistd.h>
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122       Portions of this text are reprinted and reproduced in  electronic  form
123       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
124       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
125       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
126       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
127       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) In the
128       event of any discrepancy between this version and the original IEEE and
129       The  Open Group Standard, the original IEEE and The Open Group Standard
130       is the referee document. The original Standard can be  obtained  online
131       at http://www.unix.org/online.html .
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133       Any  typographical  or  formatting  errors that appear in this page are
134       most likely to have been introduced during the conversion of the source
135       files  to  man page format. To report such errors, see https://www.ker
136       nel.org/doc/man-pages/reporting_bugs.html .
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140IEEE/The Open Group                  2013                             PIPE(3P)
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