bsd/man/man2/pipe.2

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  34 .\"     @(#)pipe.2      8.1 (Berkeley) 6/4/93
  35 .\"
  36 .Dd June 4, 1993
  37 .Dt PIPE 2
  38 .Os BSD 4
  39 .Sh NAME
  40 .Nm pipe
  41 .Nd create descriptor pair for interprocess communication
  42 .Sh SYNOPSIS
  43 .Fd #include <unistd.h>
  44 .Ft int
  45 .Fn pipe "int *fildes"
  46 .Sh DESCRIPTION
  47 The
  48 .Fn pipe
  49 function
  50 creates a
  51 .Em pipe ,
  52 which is an object allowing
  53 unidirectional data flow,
  54 and allocates a pair of file descriptors.
  55 The first descriptor connects to the
  56 .Em read end
  57 of the pipe,
  58 and the second connects to the
  59 .Em write end  ,
  60 so that data written to
  61 .Fa fildes[1]
  62 appears on (i.e., can be read from)
  63 .Fa fildes[0] .
  64 This allows the output of one program to be
  65 sent
  66 to another program:
  67 the source's standard output is set up to be
  68 the write end of the pipe,
  69 and the sink's standard input is set up to be
  70 the read end of the pipe.
  71 The pipe itself persists until all its associated descriptors are
  72 closed.
  73 .Pp
  74 A pipe whose read or write end has been closed is considered
  75 .Em widowed .
  76 Writing on such a pipe causes the writing process to receive
  77 a
  78 .Dv SIGPIPE
  79 signal.
  80 Widowing a pipe is the only way to deliver end-of-file to a reader:
  81 after the reader consumes any buffered data, reading a widowed pipe
  82 returns a zero count.
  83 .Sh RETURN VALUES
  84 On successful creation of the pipe, zero is returned. Otherwise,
  85 a value of -1 is returned and the variable
  86 .Va errno
  87 set to indicate the
  88 error.
  89 .Sh ERRORS
  90 The
  91 .Fn pipe
  92 call will fail if:
  93 .Bl -tag -width Er
  94 .It Bq Er EMFILE
  95 Too many descriptors are active.
  96 .It Bq Er ENFILE
  97 The system file table is full.
  98 .It Bq Er EFAULT
  99 The
 100 .Fa fildes
 101 buffer is in an invalid area of the process's address
 102 space.
 103 .El
 104 .Sh SEE ALSO
 105 .Xr sh 1 ,
 106 .Xr read 2 ,
 107 .Xr write 2 ,
 108 .Xr fork 2 ,
 109 .Xr socketpair 2
 110 .Sh HISTORY
 111 A
 112 .Fn pipe
 113 function call appeared in
 114 .At v6 .