bsd/man/man2/pipe.2

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  34 .\"     @(#)pipe.2      8.1 (Berkeley) 6/4/93
  35 .\"
  36 .Dd February 17, 2011
  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 .Fo pipe
  46 .Fa "int fildes[2]"
  47 .Fc
  48 .Sh DESCRIPTION
  49 The
  50 .Fn pipe
  51 function
  52 creates a
  53 .Em pipe
  54 (an object that allows unidirectional data flow)
  55 and allocates a pair of file descriptors.
  56 The first descriptor connects to the
  57 .Em read end
  58 of the pipe;
  59 the second connects to the
  60 .Em write end .
  61 .Pp
  62 Data written to
  63 .Fa fildes[1]
  64 appears on (i.e., can be read from)
  65 .Fa fildes[0] .
  66 This allows the output of one program to be
  67 sent
  68 to another program:
  69 the source's standard output is set up
  70 to be the write end of the pipe;
  71 the sink's standard input is set up
  72 to be the read end of the pipe.
  73 The pipe itself persists
  74 until all of its associated descriptors are closed.
  75 .Pp
  76 A pipe whose read or write end has been closed is considered
  77 .Em widowed .
  78 Writing on such a pipe causes the writing process to receive
  79 a
  80 .Dv SIGPIPE
  81 signal.
  82 Widowing a pipe is the only way to deliver end-of-file to a reader:
  83 after the reader consumes any buffered data, reading a widowed pipe
  84 returns a zero count.
  85 .Pp
  86 The generation of the
  87 .Dv SIGPIPE
  88 signal can be suppressed using the
  89 .Dv F_SETNOSIGPIPE
  90 fcntl command.
  91 .Sh RETURN VALUES
  92 On successful creation of the pipe, zero is returned. Otherwise,
  93 a value of -1 is returned and the variable
  94 .Va errno
  95 set to indicate the
  96 error.
  97 .Sh ERRORS
  98 The
  99 .Fn pipe
 100 call will fail if:
 101 .Bl -tag -width Er
 102 .\" ===========
 103 .It Bq Er EFAULT
 104 The
 105 .Fa fildes
 106 buffer is in an invalid area of the process's address
 107 space.
 108 .\" ===========
 109 .It Bq Er EMFILE
 110 Too many descriptors are active.
 111 .\" ===========
 112 .It Bq Er ENFILE
 113 The system file table is full.
 114 .El
 115 .Sh SEE ALSO
 116 .Xr sh 1 ,
 117 .Xr fork 2 ,
 118 .Xr read 2 ,
 119 .Xr socketpair 2 ,
 120 .Xr fcntl 2 ,
 121 .Xr write 2
 122 .Sh HISTORY
 123 A
 124 .Fn pipe
 125 function call appeared in
 126 .At v6 .