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1 .\" $NetBSD: pipe.2,v 1.6 1995/02/27 12:35:27 cgd Exp $
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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 .